i dont keep up on this stuff so maybe i am missing some context.

should he have been obligated to stay at google for the rest of his career?

Google essentially (but not exactly) aqui-hired Shazeer from character.ai in a deal that cost them $2.7B, with Shazeer personally making something in the region of $1B from it. Presumably there was some sort of retention period specified in the contract (you are not going to pay $2.7B to hire someone, then let them leave with no penalty the next day), but in the event Shazeer only stayed for 22 months before now leaving. Maybe he paid some penalty for leaving, but if so presumably more than compensated for by OpenAI.