Looking at the map of travel restrictions by country, one can see that Mexico and Colombia are truly unique:
They're currently the only nations not requiring a COVID test prior to arrival and not restricting visitors from any nation in the world, as long as they have a visa-free passport or Mexican visa. Mexico is especially unique because it never required a COVID test and never restricted travel from any nation, though hotels weren't allowed to rent rooms to tourists until June 2020. How was this approach to border controls justified internally, given the immense pressure to conform to what other countries are doing? Did the Mexican government ever explain their justification for keeping the border open no matter what?
NB: While the Mexico->US border is officially closed, the US-> Mexico border was always open.