For me and my tables I run I've seen a few notable truths which have shaped how I run things. And I expect these truths are probably true at a lot of your tables too...
1) None of my players are artistically capable of roleplaying an actual alien species, nor do they want to. Every PC regardless of race ends up being portrayed as a "human in a rubber mask".
2) As far as roleplaying is concerned... Races aren't actual alien species, they are merely packages of human quirks bundled together to create a specific personality type. And when players want to select a non-human race, it's really because it is easier and more justifiable to play that personality type via that non-human Race, than it is to play a Human who has the same package of quirks. A player could play the "drunken, grumpy
jerk" personality as a Human... but because it's a fantasy game they see that personality type as the Dwarf's domain, and thus want to play a Dwarf. Which explains quite well why all the Races have one dominating and stereotypical personality type for every member within it, because the Race is merely the shorthand for the personality package.
3) Players for the most part enjoy trying new things, but are also amenable to being restricted in certain places when they have had in the past and will eventually have again in the future the opportunity for trying those new things. Which is why I purposefully do not run all my games in one single setting-- every campaign jumps around to a new setting (or a new section of a previously-played setting) each time. Because each setting has its own specific dominate races/classes/backgrounds, there are always new things to choose that actually work well for where we are playing. And they know that if my current Theros game is humanocentric, they are okay with going along with it because they got to play whatever goofy-ass option they wanted for the Forgotten Realms game, and will have an entirely new set of options if/when we play the Feywild game down the line.
And finally 4)... Practically none of my large group of players wants to DM, so they all know that if they actually want to play in my game they go along with whatever it is I've set up this time around. Because they quite possibly could be on the outside looking in if they put up too much of a stink.
Mod Edit: Language use. ~Umbran