Of all the apologetics around pay gap, I think this is the one that many people could agree is the least fair. The company knows you're worth more, they can feasibly pay you more, they pay someone similarly skilled and talented more. But they do not simply because of a conversation at the very beginning of accepting a role (and once a year). Talk about an abusive angle. That's like saying to a child "Oh you could have got a PS5 and a game for your birthday, but you only asked for a new game for your ps4"... Employers should be seeking ways to retain talent and underpaying is a ticking timebomb.
The cost of rehiring is MASSIVE:
ad/promotion cost for the role(indeed), at least 100 hours of interview time (across candidates), 1/3rd the salary to the recruiter, 3-6 months of gradual training before they're "highly productive", losing 1-3 months of adopting team's productivity to training that person, losing the institutional knowledge of the outgoing person. Losing the opportunity of having a tenured person to promote into a higher level that is even more expensive to hire for. Not to mention the opportunity cost of the work that could have been done (eg if instead all those resources made your product better)
It's asinine to think someone would risk losing an employee over $20k when those costs above easily amount to 10x that.