"Why doesn't everyone like something?" People have different motivations, ability, and interests and are not a hive mind.
This is not simple to boil down to just "bads being bad" or "entitlement". And this isn't even really a parser issue though it can tangentially relate to it. I certainly enjoy the harder fights that I have done but don't like doing them without people I know and can trust will be competent and have fun with it if something goes wrong. In short I don't like doing tough fights with randos, that's my (admittedly slightly unreasonable) reason for not being up to date on content. Does this mean I hate those fights? Nope.
Some people do however want all content accessible to all ranges of skill and as someone who's done many "unfair" challenges in gaming, I think that's simply impossible. There has to be a nature of exclusivity in content and/or reward for those that want to rise up and put in the effort. And that means the easier content won't always reward comparable things at the same pace or even at all. That's okay and most people, even the anti-parser crowd, agree with that.
Not liking certain content doesn't automatically mean that they want it gone or dumbed down it's just something they don't care for and would like resources poured into content they DO like first rather than second. Like most humans.
I feel like OP missed the point or is taking some leaps in logic regarding how certain groups view certain content. Reasonable arguments are incredibly easy to see if you take a step back and you can quickly dismiss the strawmen and actual hard-headed players. You cannot, I repeat CANNOT, judge one group by a vocal minority especially when that minority seems to already be fractured into conflicting views. Read any vent thread and you'll quickly see everyone's experiences vary and to try and draw any sort of trends are shaky. I've been hearing about "ice mages" for years but have literally never seen one. But others have. I hear that only bad players don't want group parses but from what I've seen argued, many types of players don't care for that system and desire another. And those that demand changes be made/not made or they'll leave, well...they need to get a reality check, calm down, and maybe try thinking from the "other" side's point of view.
Are there elitists in harder content? Yeah sure there are. And there's elitists in easy content. Crappy people will be crappy people regardless of where you see them and should in no way influence how you view that part of the community. Hell even the phrase elitist has become so watered down that it's better to just call crappy players for what they are: crappy human beings. And that category includes those who can clear Ultimate and those who single-target a pack of 10 mobs cause reasons. I'm sorry if it sounds like I'm saying stuff that deserves a "well DUH" but that's really how simple it is. At least to me
TL;DR: Not everyone has to like the same content and everyone has their multifaceted reasons for doing so. That's just how it is.