I would summarize this effect as BigCorp HR being much more disciplined/constrained on individual compensation than the M&A department. Naturally, well-positioned and clever employees will capitalize on this.
Google was already at the center of the high-tech employee wage-fixing earlier this decade, so filing lawsuits to create deterrence wouldn't be that surprising.
https://en.wikipedia.org/wiki/High-Tech_Employee_Antitrust_L...
Between these, which do you think is more likely?
Or, CEOs don't have the same set of options engineers have, or, CEOs are drawn from a pool with different preferences than engineers have, or...
Well, lots of other reasons your dismissal of the claim about engineers based on CEO behavior is unconvincing.
Learn everything.
I have a goal, it is to be better than average at every "skill".
Plus, yes, there are other goals than "not working".
I expect a startup was the only option to execute on the idea with a decent level of autonomy. Google/Alphabet already have well established teams in the areas of mapping & autonomous driving so you can't just go ahead and start your own multi-engineer effort.
If the difference was more subtle such as 2 to 3 times X, then the incentive to go through this much trouble to retain much of the value you create is much smaller.