EDIT: Moreover, I think that essentially what Google is doing here is having you sign away things which they otherwise could, and would were the assignment provision not permitted to them, simply prohibit outright via a during-employment non-compete, which even California (with it's unusually firm stance against post-employment non-compete) is generally fine with.
Criticizing the notion of "own time" when the people who effectively have the power, and the greater share of organization (both extant and allowed), perpetuate that notion seems like a less-than-useful use of time.
In the state of California, there very much is strong protections for workers intellectual property.
And the courts do not share your opinion on what is someone's "own time" or not. The courts instead protect workers.
It is possible that Google has made its employees sign some illegal contracts, that aren't enforceable in court. But if this stuff theoretical went to court, the law sides with workers.
They can quit if they want time that the employer does not deign to grant them.
In my more cynical moments I think this is the prevailing view in American tech.