I'm trying to see any disadvantages for countries that do this

One unintended consequence could be that while a country might get some foreign citizen remote workers, it would decrease the remote working opportunities of their own citizens.

E.g Spain might think "we'll get Americans to move here and do their U.S jobs" but what they actually get is, for example, Moroccans getting U.S jobs from Spain and more less chances of Spanish citizens getting U.S jobs.