Should the employer pay for someone to commute 4 hours? How about a 2 hour flight everyday? This is all arbitrary, but it is much simpler to just let the market sort it out.
Employer offers $x for employee to be in y place at time z. Employee figures out if $x is enough to incentivize them to be there at the time, and otherwise asks for more money or seeks other employment.
If employer does not find sufficient employees at $x, then they have to increase.