When I graduated in '98 the most "cool" thing was to work for the biggest name possible (so Microsoft or IBM at the time), but I imagine things have changed.
In fact it seems like some sort of perversion of the Protestant ethic where instead of undeserved salvation being witnessed by material success through hard work, so-called intelligence and maturity—“ironically” acknowledged to be the fruits of privilege and good fortune—are evidenced by holding reactionary (“centrist”) views and by taking these sorts of jobs.
This accounts for many of the upper middle class new grads I see (kids who couldn’t guess how much their family earned within 100k and wouldn’t see that as unreasonable).
When it comes to lower income or many international students, there is definitely an advantage to the Google/Facebook brand on your resume, magnified when you are talking about using your resume overseas. And of course in that case or if you expect to have to pay medical bills for aging parents soon it is a grand sort of luxury to turn down such a job offer.
The consequence, ironically, is that both the fashionable cynics as well as the idealistic new grads who turn away from Google/Facebook thus end up being mostly affluent and (debatably) largely white. Go to the careers page of some social-good startup and check out their photos!
That covers the pull factors I’ve seen. In terms of push factors you have to also account for Google/Facebook just having an order of magnitude more recruiting money and brand recognition.