Still some of the remote-only companies remained constrained to citizenship and legal right to work in the company's HQ country.
Labor law is local. If you hire someone in a different country (say, Sri Lanka) and things go south for whatever reason, they can sue you in the relevant local court.
To re-emphasize: by hiring an employee in that country, you've submitted yourself to the jurisdiction of the labor courts of that country. This supersedes and replaces any language you might have in the employment contract about the jurisdiction of employment.
Of course, enforcement is a problem. If a court in Sri Lanka issues your company a summons and you ignore it, the legal consequences will be limited (although you might be arrested if you ever visit that country). However, if that employee is located in a major country or bloc (e.g., the European Union), not being able to travel there ever again is a high price to pay.
In nutshell, this is why many remote companies are careful about hiring in foreign jurisdictions. The potential legal complexity is probably not worth it.
The con is that (as an employer), you'll have to require each individual employee to incorporate their own LLC and contract out their services that way. For obvious reasons, I can see more than a few employees giving this a pass.