For small businesses and small startups it's still non-trivial to hire out of state, in terms of legal and tax overhead.
All states require that you register as a company there and pay taxes.
There are PEOs like Justworks that act as the employer and file taxes for you. But you still have to register first and then assign the company to the PEO.
In short it varies a lot and that doesn’t take into account things like local laws on compensation.
I say this as a founder of a remote-first startup registered in 12 states.
That also doesn't address that it is significantly cheaper for group health insurance in the US vs. individual. As a company I can be paying $400/mo vs. the employee who would be paying $2K for similar coverage.
It’s unfortunate because this system encourages hiring remote offshore contractors.