It's a version of the prisoner's dilemma. They could do that, and they arguably should do that. But it won't scale to everyone doing that, and so it breaks down to a remote person with lower cost of living volunteering work for a bit less, in order to secure a desired position for themselves.
So you are indirectly saying that they will form a union. Human greed will say that the developer in Seattle(or others) will not agree to it and look for a better deal for himself/herself.
what if you had wheels instead of feet? there is zero mechanism for this and tech workers have shown again and again that there is not interest in a professional union.
Unions in the US have policies that tech people do not want. Often they are backed up by law, so you cannot legally form a union that gives you the good without the bad.