It’s seems like that’s often the case nowadays. Anyway, that’s not saying, though, that there aren’t areas so mixed that it looks like Star Trek. Some of those places are airports. Others are the Itaewon District in Seoul, South Korea, and parts of NYC. A more realistic ethnic makeup for movies would have one dominant ethnic group with a few characters outside that group. That would be way more believable and seem less like it’s pushing a social agenda.
Some areas would have more of an outside ethnic group in the mix than others due to the need for a realistic portrayal of the area. For instance, in Appalachia, you see quite a number of Blacks here and there at a supermarket, and in more Deep Southern areas, in a lot more places than that.
However, a lot of Asians is one thing you won’t see in the South generally, outside Atlanta and places like that.
New York City etc.
Those areas might really be as mixed as TV shows set in the area portray, but those shows still alienate people in much of the US, as their areas are not that mixed.