No company actually does this, they are just bloated because they have so much money and managers rank/value is determined by how many people they manage.
They explicitly did this in the 00's. Some circles of top companies over a decade ago were convicted for having anti-poaching agreements amongst each other.
May be a bit different now (as others said, free money is gone, so competition cropping up is much harder to do and much less a concern), but the tech boom of the 2000's very much worried about becoming the next MySpace to some startup's Facebook. That's why tech salaries became so high to begin with.
The anti-poaching thing was something completely different. That was preventing other companies from hiring people away from them because they were useful employees, not hiring people to prevent them from competing. Also, anti-poaching agreement kept salaries lower, it didn't inflate them.
It goes both ways. They can't collude woth hundreds of studios so they offer top salaries to out-compete the bulk of competition. Then for the remaining studios who can pay, they sign the agreements so they don't keep trying to one-up each other. Which would be bad for their business if they start trying to bid 300k for every worker (which may be what they deserve, but companies will always penny pinch).
>That was preventing other companies from hiring people away from them because they were useful employees, not hiring people to prevent them from competing.
Aren't these synonymous? You either entrap a necessary employee with contracts and/or absolute top compensation becsuse they are useful or even vital. No one's colluding to keep a janirot wage low (well, society is, but it's no one entity you can sue).