Who would have predicted that Leningrad would make a comeback in the 23rd century?
I think the main reason for the lack of Earth-based diversity is pretty simple: Star Trek is, as things stand, a Western show aimed at Western audiences. Studios and directors share a fear, most probably unwarranted, that moving the focus away from Europe or North America will alienate vast swathes of the public in those two continents.
Of course, this is a damned stupid assumption. Setting a scene in future Tokyo or future Beijing would have no impact on the film's reception in the West, but it will boost the Box Office numbers in South East Asia.
To be fair, they are destroying those Western cities. I'm sure Asian fans would rather not see that happen to their cities in a movie (Godzilla did enough in Tokyo).