You can change these contracts. Hiring people is difficult and once the company has made that decision they don’t want to lose you over a contract clause.
It’s anecdata on my part but whenever a white collar worker tells me they don’t need a union because they can negotiate a better deal, they get real angry at me when I ask them the last time they negotiated a better deal for themselves
I am good at what I do, but no unicorn and not FANG "level".
But then again, I don't live in the US