I'm not sure I understand your argument here. If we cut through the clutter, you're essentially advocating that you hire people on an individual basis and shouldn't weight at all what school they come from. No?
I know someone who dropped out and is now making plenty of money at a software development gig. I also know CS grads who can't think about anything outside their little realm to save their lives. Point is: some schools legit don't filter well for learning capacity.
I feel pretty comfortable with my interpretation.
If you find an efficient + effective way to compare all the applicants, that would make it easier to put everyone on the same footing regardless of school. But that's hard to do and it's easy to be risk averse and just hire the Harvard grad.
A Harvard grad presumably costs you more, but they keep doing it that way because 1) it's simple, and 2) if you try to hire more broadly but misjudge and make a bad hire, that's potentially much more expensive.
Even if they're making CRUD apps, making tons of high-availability CRUD apps that work against dozens of services your team doesn't own that can serve huge fractions of the globe requires non-trivial coordination and skill. (Not that all those companies do is CRUD apps, but even if.)
I'm not sure it's as jard as those companies make it out to be -- but it's not "just CRUD apps", it's the logistics of CRUD apps spanning the globe.
Source: work at one of those companies.
Sure, there are software jobs where you're setting up wordpress blogs, but there are plenty that require you to think about algorithms and how your database actually works in order to do them well.
These companies set the bar at 70+ for a number of reasons. Their own egos ("I only work with 'the best' so therefore I'm also 'the best' and don't want to water that down"), status signalling for the companies, to keep bright young talent from starting a competitor, etc.