I'm starting to think Google (probably Facebook too) scoops up top talent simply to deprive potential competitors (e.g., startups) of the resources they would need to challenge them. Actually having something for them to do is secondary.
I have believed this for a very long time. Both Google and Facebook are well known for hiring top talent at top dollar and then putting them on projects that are far below their ability level. It takes that talent off the market.
Yea, hard to believe great engineers would be happy that way. They apparently can't even have side/personal projects to scratch that creative itch if the day job isn't providing enough challenge. But leaving or doing a startup would result in a big drop in pay (at least initially). Easy to see how burn-out happens under those conditions.