At least two reasons:

1. It's been the default answer for millenium, and there has only been pushback on this for the last 50-ish years.

2. Because individual variation is often larger than the group variance?

3. (Related to 2.) Because it's often not a useful answer. E.g. Suppose it were proven that women were worse at math than men. Would that change how we taught boys and girls? It almost certainly would, and it almost certainly would be detrimental for the little girls. [note: There is a lot more that could be said here, that I won't say because it would take too long]

These aren't reasons to not do the research, but they are reasons that we should be deeply suspicious of research that satisfies our cultural biases.

Political correctness gone mad.

There was a law passed in the EU last year, which made it illegal to "discriminate" based on sex when giving out insurance.

So that means you're not allowed to give men cheaper life insurance, even though men live shorter lives than women, and you're not allowed to give women cheaper car insurance because statistically they're safer.

It's complete BS.

I also find it funny how if you tried to argue that homosexuality wasn't something "hard wired", you'd have a pretty tough time. But if you argue "being girlie and liking girlie things" is "hard wired", you have an equally tough time. It's all political "equality".

I think people will look back at this time period as very odd. Trying to pretend everyone is "equal", rather than embracing their differences, strengths and weaknesses.

This is a sensitive topic, like global warming, because it degenerates into politics rather than science. A study value is based on how well it supports preconceived political views.

American slave culture was "scientifically" supported by studies demonstrating the inherent inferiority of the Negro race. (Indeed, that's what race theory is.) This is the same kind of motive behind the search for the "gay gene" or the claim that there are no homosexual non-human animals.

It's obvious there are inherent differences between boys and girls. The question is: how far does it go? People are sensitive to the issue, because other people are liable to read a lot more into whatever scientific evidence exists than is warranted.

For example, it is very typical here on HN for people to say that "there are biological differences between men and women, so maybe women just don't want to work in programming?" Let's admit that the premise is true. Does that mean the proposed corollary is true? No, but that doesn't stop people.

People misuse facts about biological differences between men and women to justify preexisting prejudices. For example, people always point to gender differences to justify why there are fewer women in programming. But even if we accept the premise of stereotypical gender differences, why does that lead to the conclusion that the preference should skew for men? To me, it seems programming is more consistent with what we stereotypically think of as work more suitable for women: involving extensive social coordination, long-term attention to small details, etc. To use the "hunter/gatherer" analogy that is so often trotted out for this purpose: programming is a lot more like working in a group to nurture a field of wheat than setting out on your own to take down a mastodon in a short spurt of bloody combat (well maybe demo coding is like the latter, but shipping quality production software is like the former!)

In summary, people read a lot more into sex differences than are justified by the data by itself, and use that information to validate existing prejudices. That's why people get defensive about such studies and try to put the results into context proactively.

Imagine a scientific study that just said "Scientific justification for social oppression found." In a nutshell, I believe that's why.

It's not even that it's bad for there to be differences between the sexes; what's bad is that some people will inevitable take these studies as justification for their sexist views and attitudes.

I'll ask the corollary question: why are people so keen to accept and propagate the wisdom from dodgy studies that tell them that the current status quo is the natural and "right" way for things to be?

Because it could be used to justify discrimination. I don't believe that but I think that's the reasoning.

Because people are quick to generalize from statistical averages. And because they're more likely to do that when it comes to women and minorities.

Consider the following: Color blindness is generally the result of an X-linked recessive disorder, meaning that it is much, much more likely to occur in men. Yet nobody thinks that one should generalize this to mean that all men (or even a majority of men) have a problem with that or that men as a rule need to be treated with suspicion for all kinds of jobs where that may be an issue.

Now consider mathematical aptitude, which very likely may not be linked to biological sex at all, and if it is, the difference is extremely small (one way or the other). But every single study that shows that men may (may!) have a very small higher aptitude at math quickly gets generalized into meaning that "girls are bad at math" [1], resulting in women being treated as less qualified for STEM jobs/education, etc.

When you've seen this pattern play out too often, you start getting sick of pop science journalism playing up one single study as a definitive result. It's already annoying in general because this is not how science works, but when it's then further used to reinforce cultural stereotypes, it's very frustrating.

Don't get me wrong: There are differences that are linked to biological sex other than reproductive equipment (X-linked disorders are a simple example). But there's a really huge amount of shoddy science and/or uncorroborated studies that pop science journalists publish selectively; they are not the same as a well-corroborated scientific theory such as evolution.

The Larry Summers kerfuffle is a case in point. The problem with Summers' talk was not that it's impossible that men are more likely to be at the extremes of IQ (both good and bad) than women. The problem was that Summers was treating an uncorroborated hypothesis (1) as established science and (2) as an excuse to have fewer women in leadership positions.

To be clear, the hypothesis – and it's an old one [2] –, is not per se unreasonable. It relies on two assumptions: (1) That a large part of IQ-related genes are on the X chromosome and (2) that the lyonization process averages out their effect in women. Which would mean that men are both more likely to have extremely high and extremely low IQ.

Lyonization, or X-inactivation, is what happens if you have a cell with two X chromosomes. Only one of them can be active, so during embryonic development in mammals, one of them for each cell is randomly and independently deactivated (except marsupials, where it's always the paternal X chromosome). This is, for example, why even women who are carriers for hemophilia (an X-linked disorder) are unlikely to suffer from it: while some of their cells have the defect, enough of their cells still produce the necessary clotting factors (though, because the process is random, that may not always be the case).

If the same held for IQ, it would be possible for a similar averaging process to take place there, too. One problem with that hypothesis is that it has not really been conclusively shown so far (it is really, really hard to get rid of the cultural factors to determine very small changes in standard deviation). Another problem is that this is a very simplistic assumption of how IQ is developed. For example, if the model were that simple, then men with Klinefelter's syndrome (who have two X and one Y chromosome in each cell, and whose cells also undergo an X-inactivation process) should experience a similar averaging for their IQ: Instead, Klinefelter's syndrome is held to be responsible for a drop in average IQ of nearly one standard deviation (compared to both men and women). So, it can't be that simple. In fact, while the brain structure for men and women IS different (in ways that we don't fully understand yet), these differences do not seem to relate to the presence or absence of a lyonization process.

So, while the hypothesis is not per se impossible, the president of a research university should really know better than treating it as established science and essentially saying, "it's just normal that we have more male professors".

[1] Obligatory xkcd: https://xkcd.com/385/

[2] R. Lehrke, "A theory of X-linkage of major intellectual traits."