Not sure why fantasy races have to have the same diverse makeup as god damn los angeles.

The problem with turning every place into a melting pot is that it implies an ease of travel. The modern world can have the average person travel hundreds of miles per day, but people notice (as much as they want to deny) that it doesn't make sense in a medieval fantasy setting where almost everyone is still traveling on foot. Not to mention how many places would be expected to have tight restrictions on immigration.

If the Dragon Age setting was established to be a place of fast and frequent global/national scale traffic, it wouldn't be a problem. But that's not the case, where even the exalted Grey Wardens are forced to walk and camp in the woods and the closest thing to multiculturalism is the Super Commies nation run by the Qunari.

There is a thing called "verisimilitude" where something needs to appear to be real even if it's not real. You see a dragon in a movie or show and it needs to look like it's a real creature, you can't have a bunch of shitty CGI that make it move like a nonexistent hologram and say "but dragons are fictional maybe dragons just look like shitty CGI hurr". People's brains won't accept that.

Similarly, having several different irl races among several different (fantasy) races like it's a New York public school is fucking with the verisimilitude of the setting because it implies the civilizations have widespread modern ease of travel.

If the places were always like that, then there wouldn't be all these different skin tones people would be far more blended due to hundreds/thousands of years or race mixing. But the characters don't have planes, trains, or automobiles and in Dragon Age even transport magic is extremely limited or else it would have been piss easy for your characters to travel around in previous DA games.