Employers in Canada don't actually need (or don't actually want) top developer talent. If they did, they would try to compete with US companies on salary (among other things).

I agree that "remote (US only)" is completely baffling. Hiring from a global talent pool instead of a local one is a huge advantage. Yes, such an employer has to deal with tax headaches but if they want to hire locally from a global talent pool, they will have to deal with immigration headaches which are much worse for the US.