The organisation that is collating the genome data for the WHO (I forget the acronym) put Thailand on the bad boy list for not reporting enough data. Without sufficient surveillance and reported data, a new nasty variant of Covid might go unseen and then be spread by travellers. That (I think) is the primary logic for keeping some nations, including Thailand, red listed.
That it's been 8 months now since any significant new variant was last detected, and the scientist in charge of the AZ vaccine project is now publicly saying that she does not expect any new and dangerous variants to emerge now - should.. hopefully.. bring an end to the red list.
On the other hand, why the heck is a country like Thailand, well developed in terms of medical facilities, not reporting sufficient genomes?