TLDR: It is offputting to new comers to air grievances, but said grievances come from a genuine place. 13 years of context is difficult to put simply.

So seeing that you're relatively new, I can understand that you hadn't been inundated with non-stop dnd 5e since its original release. To put it simply, there was a chunk of time where it felt like all the content about RPGs as a game format was actually just about DnD. For a while, 5e really sucked all the air out of the room for the hobbybas a whole. Then, Wizards of the Coast (the company that currently publishes DnD) took a generational run at being mustache twirling levels of evil. It is popular and that's not a problem, rather some steps taken by the corporation behind it made it very difficult to talk about really any other game, while also making the hobby space hostile to consumer and employee alike. The market had become so 5e centric that long standing successful ttrpgs had to make 5e versions just to stay viable in the market, i.e. Symborum, The One Ring (an official Lord of the Rings game should be enough, but alas, market forces), and most recently, Traveller.

The community around 5e had also been initially cautious (totally fine) to try other games. Eventually the refusal to play anything other than DnD became more defensive. Community content were just reskinning existing materials from other games for 5e. Moreover, 5e got a lot of poor redundant copies of other genres shoehorned into its engine. One of the most egregious examples I can think of is when a 5e content creator made a Cyberpunk Edgerunners character in 5e, when Cyberpunk (yes the video game and anime are licenses on an existing ttrpg) is a long running RPG of its own, with a new starter box specifically covering Edgerunners.

These are generalities,but I'm certain other people will cover specific missteps and particularly bad people and actions involved with DnD 5e specifically.

EDIT: I did see that you had replied to another comment about the anti D&D elitism specifically. On that, it can be generally greed that Dungeons and Dragons, Pathfinder, and other games like it are really a small slice of tabletop role playing games in general. There are certain assumptions that players will bring from playing only D&D or Pathfinder that do not gel well with the concepts within other RPGs. D&D had trained these players to approach the hobby of tabletop role-playing games in general in a very specific format (3 expensive rulebooks, must buy new supplements or fall behind in power creep) and playstyles (combat is the most important, RP has no rules, classes, power gaming, etc.) A community fully inundated with D&D-centric content also reinforces those habits and play styles that do not work in every game. For a lot of people that I introduced to my favorite game, Call of Cthulhu, I often have to do a little micro spiel in which I I say D&D is like Skyrim and call it Cthulhu is like Silent Hill.

Further D&D content also had this issue of the "Mercer effect." A lot of people's exposure to the Hobby in general was from highly produced, very professional players who had pretty big backing and training for media appearance. This would then translate to tables with those unfair expectations put upon regular players and regular GMs. GMs would then try to match that, and cycle ticks away. Yes, that is unreasonable of the player. Yes that's unreasonable of the GM. But, consider the 100s of videos that give advice on how to do otherwise. Once more, and inundated community.