Yeah, good luck being the odd one out who wants special individualized contract. This might work for unicorn value level employees that are poached from one FANG to another but not for the average Joe.
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