I think they wanted to give Namor a more post-colonial flavor to match Wakanda. The problem with Atlantis/Lemuria/Mu is that these are turn of the century European ideas (and are inturn influenced by paternalistic European ideas as well as colonialism/imperalism) and having an ancient ancestral race with Mayan aesthetics/terminology is just problematic and suggests that indigenious people of Latin America didn't have their own civilization and had to be "given" it by another ancient race. Much like the unfortunate connotations with the ancient aliens conspiracy ideas about indigenious peoples in Easter Island/Latin American/Egypt/Middle East had to be helped by aliens in constructing their monuments.