>Uncommon races are just a roleplaying crutch
Maybe the players are just sick of the core d&d races.
I can get behind that.
I'd rather play as hobgoblin, Githyanki, or non-op half-dragons, or more monstrous things like minotaurs, centaurs, and fauns, then yet another goddamn core race, because for the most part, I've just gotten sick of them myself.
I don't need to be a race that's super rare in a setting. I'm just sick of the stock races. When I gm, I often drop most of the stock races and dont allow them at all (as in this setting has no Elves /dwarves /half Elves /half orcs /halflings /gnomes) instead picking a different set of less commonly used fantasy races that havent been so done to death and over-troped.
Tl;dr: change which races are common and then your players can play a "common" race without it being the humdrum same old shit they've seen a thousand times.
>Tiefling?
The Hells and abyss have established major *countries* on the continent, and the true demons/devils tend to be at the top, whereas demihuman blooded fiends tend to be the average citizens.
Done.
>Hobgoblins?
Hobgoblin warmongering expansionistic empire, perhaps with a propensity for selective breeding based on desired traits, with a highly rigid social structure.
Romans+china+andromeda nietzcheans.
Done.
>Orcs
MongolHunVikings, or maybe VikingNativeAmericans.
Done.
>Want more variety than existing d&d races, but don't want to make something up?
Lift something from another setting/game.
Include a medieval version of a mass effect/starwars race. Or lift something from a different fantasy setting, like vedalkans, or phyrexians, or gorons, or worens, or whatever the fuck. Etc.
Done. Problem solved.
Suddenly it's not all the same tolkien goodguy races again and again, but something different. Variety is a good thing.
I can see how a player who has to go for "rare exotic races" to get variety is likely to do so.