I really don't see how adding Wookies and Klingons to a Gothic horror game like Curse of Strahd works at all and still maintains the tone and themes of the setting. To me that is just as jarring as having machine guns in a D&D setting that is fantasy medieval/renaissance like Forgotten Realms.
However, even without such jarring choices, you can see that certain races can be a poor fit for general adventuring. It is why you don't see any Large races and the two semi-large races they attempt to shoehorn into a medium frame (centaurs [UA] and goliaths, for example).
To look at Dark Sun, a centaur race would be a poor fit (human/horse hybrid). Could one be shoehorned in? Maybe, but it would still be out of place. A human/scorpion hybrid would be a better fit as it doesn't require the setting to also import other creatures to support it.
Would gnomes work? Maybe, but they would require the same extensive rework of culture that halfling received to fit into the setting. Maybe that isn't something a DM wants to take on top of all of the other parts to consider?
I suppose it can all be hand-waived away if all anyone cares about is rolling dice. However, I have played in a large number of RPG systems that are more character and story focused than D&D has been in the past.
To me certain groups of races also just don't work. For example, placing a Yuan-Ti into a party, if role-played well is going to be strange unless everyone else in the party is willing to be submissive (i.e., lackeys) to the Yuan-Ti character. The same really goes for Drow as well. Really how many outcast Drow characters are there really before it becomes cliche?
Ravenloft is probably one of the best examples you can give. However, as presented, even in the 2E days, its nature left it open to all playable races and classes from just about any of the existing settings.
Sure, a fantasy version of the Wookie is not a great fit for the setting; but is a halfling or a dragonborn really much better? And do you think it's impossible for a player to somehow make the Wookie in Ravenloft work? It may be challenging, but impossible? I could see a fantasy Klingon fitting right in....trying and struggling to face all threats with martial prowess, and perhaps being tempted by the Dark Powers....
The Large creature aspect is one that they struggle with, but as you point out, they kind of shoe horn it in. I think this is more a mechanical concern than anything else. Half-Giants worked just fine in 2E Dark Sun. But then, I think the nature of the world lent itself to accommodate them.
Regarding gnomes, what you're saying may not be required at all. The gnome in question could be the results of mutation (an element that exists in the setting), or some kind of survivor of the Sorcerer Kings' genocide, or a planar traveler. A centaur could easily be reskinned so that it is a better fit, but be mechanically the same. There are options that can avoid any intense work on the part of the DM. I don't think I'm advocating for hand-waving in favor of rolling dice; it's more a case of a DM and player working together to make sure setting concept and character concept can work together.
As for cliche, you seem in favor of it in some ways, and not in others. If an outcast drow is cliche, then certainly the monolithically evil drow is as well. And so is the gruff dwarf and the serene elf and the stoic knight and the mysterious wizard. Sure, these things are archetypical, but they can still all be used to say something. I think this is where you're really moving into personal preference; you find X to be cliche, so it shouldn't be in a game.
Personally, I've found that when a player comes to me and says something kind of crazy like "I want to play a Yuan-Ti", it's an exercise in creativity to ask why would there by a Yuan-Ti adventurer? Is he different from his fellow Yuan-Ti? Does he share some goal with the rest of the party? These kinds of questions or the ones that I've found lead to truly memorable characters and games, and that's a large part of why I tend to not restrict players in their choices.