It's interesting to see some of the responses here. They are in some cases quite defensive and/or dismissive of this observation. Some of the defenses raised:
1. Deferred altruism: "I'm making the easy money now but I'll (work on big ideas,give back,etc) later."
I question the sincerity of these statements. For one thing, human nature is funny when it comes to money. How much is enough? Most of us here aren't independently wealthy so we probably think several million dollars will do, tens of millions will be plenty. I bet you'll find many people with that kind of net worth still thinking they're poor and they need to make more. It's probably an easy trap to fall into.
People think money won't change them. For most people it does.
More to the point, the biggest motivator is the need to succeed. One reason startups are successful is it's either succeed or die. Necessity is the mother of invention and all that. I truly believe you're much more motivated and productive when your (financial) life depends on it. If you're wealthy, most of the time you're just not going to be as motivated. It's a rare individual that is the exception.
2. Big problems are hard/expensive.
No actually they're not. Some are, sure. Thorium reactors would be an expensive problem.
A lot of other problems in the fields of machine learning, bioinformatics, etc are largely just software problems. Computing power continues to get exponentially cheaper. The Khan Academy is a big idea with very little costs to entry or operational costs.
3. "This is happening in other areas too!"
Who cares? You're not responsible for anyone's behaviour other than your own. Plus of course two wrongs don't make a right.
I get the desire to strike it rich. I really do. There's nothing wrong with that. It seems disingenuous--even dishonest--to suggest there is a deeper altruistic motive. Most of the time there isn't.
I don't see Kara's comments (or mine for that matter) as a criticism of the motives of any particular individual or company, merely a lament that society as a whole places such value on what are really shallow desires and distractions. I'm sure it'd be harder to get funding for something as unsexy as, say, protein folding than it would be for creating a social network for cats and that really is sad.