Why remote roles are region specific and not 100% remote?

I always wondered, because I'm based out of India and trying to secure a good remote role, why most companies offering remote positions are region‑specific—like remote roles only in the US or the UK. Why don’t they open the doors to the entire world when they’re looking for someone to work for them remotely?

Another pro of it is people from different parts of the world will require less pay comparatively. Time difference? That's a reall issue — but anything besides South East Asia or Ocenia countries could pretty much overlap.

I mean, I'm based out of IST, I can overlap EST all 8 hours and PST close to 5 hours.

If the blocker is some regulations, why not hire on contractual basis then?

Just some things I wanted to always learn.