Narratively... if there are dozens upon dozens of intelligent humanoids in the world itself... there should be a connective Race write-up to have one of them as a possible PC. There's no reason why any one of them couldn't become an "adventurer" in the game world. So in that regard... I'm absolutely fine with WotC continually coming up with new Races for optional PCs. It makes total sense.
That being said... I also know for a fact that few if any D&D players I've ever encountered actually play any non-human races because they desire to get into the mindset of playing something "alien" to them. Rather, almost every single one has just gone the "Human in Funny Hat" route and more often than not select their race... indeed it is true... based upon the
game mechanics the Race provides.
Every single table I sit at... whether that be home games or cons or wherever... I'm never confronted with someone playing a character that does not seem human. Every single PC could be a Human so far as how the characters are played. So in that regard... I usually prefer a more constrained list because I'm a DM who enjoys having his players interacting with their Backgrounds and that often means others of their Race. And the more disparate the Racial make-up of the party is... the more far and wide I have to send the party to allow that to happen.
Trying to find reasons for a party of a Duergar, Aarakocra, Grung, Fairy, and Githyanki to not only get together for whatever reason to go adventuring, but then also meet up with other duergars, aarakockras, grungs, fairies, and githyanki is kind of ridiculous. The only somewhat useful option at that point is to design a game world where those five are the predominant Races of the world rather than Humans, Elves, Dwarves, and Halflings are, but at that point that type of game world just holds less interest to me and I don't want to run anything in it. Especially considering the fact that I know my players would play that Duergar, Aarakocra, Grung, Fairy, and Githyanki exactly the same as if they were five Humans... so what's the point?
I freely admit this is purely my own prejudices and not anything that is a problem with the game. So I'm glad WotC makes all these options available for players... I just don't usually want to play with the players who take WotC up on them.
