Usually it comes down to some people objecting to the idea of a DM setting up strict parameters without being flexible. It usually ends up with opponents of DM strictness essentially expressing that they think such DMs are selfish jerks, and are surprised anyone even wants to play with them.
I think you are taking what is typically said in the wrong way. It isn't that people are saying that a DM applying strict parameters is inherently a selfish jerk, it's that people are saying that a DM applying strict parameters
that their players would rather they not apply is a selfish jerk.
I.e. if you are a DM that doesn't want X race in your setting and none of your players have a problem with it you aren't being a selfish jerk. If you are a DM that refuses to include X race in your campaign, not even as a one-off oddity that everyone in-setting constantly is confused or surprised by, even though one or more of your players really want to play X race, maybe it's even their favorite race... then you are being a selfish jerk.
How do you feel about playing D&D with a World-Building DM?
I make it a rule to give anyone who wants to DM a chance to do so, and as much assistance as they want. Whether they want to build their own world or use one that is already established doesn't even register as a factor in deciding whether or not to play with them.
Would you enjoy playing a character in Westeros, DMed/GMed by George R. R. Martin? A character in Middle-Earth DMed/GMed by J. R. R. Tolkien?
Likely not. The skills that make one an entertaining novelist are not the same skills that make one an entertaining DM, and are actually at high risk of being counter-productive to the task of DMing
Would you ask to play a cat-person or a wookie, or a kender? Would you ask them to redefine who could and could not use magic?
What you are really asking is if I as a player would ask the DM if I could play something that isn't within the setting's definition of "normal and entirely expected." My answer is this: I'd let the DM know I am interested in playing whatever sort of character I am interested in playing, and if I want part of that play experience to be the setting responding to my character as if it were completely normal that would be in the form of me saying "Hey DM, here's an idea I had that maybe we can do a later campaign that will fit.", while if I want part of that play experience to be that my character is alien to the setting and vice versa I would let the DM know that too along the lines of "Hey DM, I'd like to play a character that isn't native to this world and setting, like someone from another dimension or planet."
In either case, if the DM didn't respond by trying to help me work that character into some campaign soon (not necessarily the one at hand), I'd consider that a negative.
I’m guessing the vast majority of people, if invited to play in such a situation, would gladly fit their character into the parameters.
Why not be willing to fit into another DM’s world in the same way?
There is a world of difference between being glad to fit your character into the "normal" parameters of a campaign, and a DM that has their world set up in a way that gives zero thought to what that DM's player group is into.
I've got a player that plays Dwarf characters basically all the time (like, he's played 1 elf, 1 human, and nothing else but dwarves for more than a decade at this point). If I want to run a campaign that doesn't involve Dwarves, I can sell him on the story of why there are no Dwarves around and he'll gladly play something else for that campaign, though he'd likely make sure that an "I'm the only Dwarf around and that is weird" character wasn't going to work first.
But if I were to say to him "I've decided that the setting we are going to use from now own, which I built myself so every decision was fully within my power, has nothing even resembling Dwarves in it." I'd quite obviously be putting what I want at a high enough priority as to completely disregard what anyone else wants (read: being a selfish jerk).
My gut tells me that the objections are, at their heart, more about believing the DM just isn’t going to create a very good world (or at least one you will like) than they are power-struggle issues.
In my view, it all boils down to whether the DM is trying to make a gaming experience suited to their players - and some DMs refusing to even entertain that the player is asking for something "oddball" without malicious intent toward the campaign.