It takes a lot of trust (on both sides) and complexity to establish a working relationship across two jurisdictions, if at all possible.

For instance, what labor laws apply? And who enforces them? And how, given parties in two different countries?

Does the company want to subject itself to some arbitrary country’s tax man or labor law enforcer prosecutions? Does the employee want to work under effectively zero labor protection? Possibly, but rarely.

It’s not even always possible, it’s very complicated to work remotely in France, for instance. The state cracks down on one person one client companies, and EoRs beyond being impractical (as they must adhere to drastic labor laws compared to the US) are in a legal gray zone.

>For instance, what labor laws apply?

The laws of the worker's locality is generally how it works. In the film industry, a production company based in LA might do a shoot in NYC- they have to follow NYC's labor laws since that's where the workers are and the work is being done.

The workers at the home base in LA have the LA laws applied to them.

>And who enforces them?

The local government.