It wasn't always like that. Mythics specifically is still relatively new in WoW's life cycle, but was supposedly added because players wanted something to do beyond just raiding and PvP. Even the relationship between raiding and PvP has been different depending upon the expansion.
Keep in mind, asking for changes because you have no interest in their preferred 'main aspect' of the game is a rather obtuse way to view it. In fact, I'd surmise that the most likely scenario you'd run into is that players saying Blizz either designed or changed the content that they loved doing into something they don't like (whether it's raiding, PvP, etc.). WoW's history is littered with such examples, and I personally feel this is one of the reasons why the game keeps losing active players. Talk to players who loved the game and quit, guarantee the most common answer you'll get is that it's just not fun anymore for various reason. Sometimes this can be a fundamental change in the player, but it can also be because the game fundamentally changed in a potentially bad direction that pushed people out of the content they loved doing.
Futhermore, this doesn't preclude Blizz from adding more stuff to do in WoW beyond just the three staples, as was the reason why there's three staples instead of two. There's even minor systems (like the pet battling) that may have niche crowds but are still very important for them. While player-driven activities is great, Blizz doesn't need to let players be the only ones to drive it. Otherwise you'll get the scenario that happened with the WoW UI being horrible for so long, as they admitted that the players would fix it with addons so why should they bother?
Tell that to Blizzard, because they'd disagree with that statement based upon their interviews and reasoning behind certain changes. They've constantly made some changes over the life of the game, some not so impactful while others are very impactful. A more likely scenario is akin to arenas: some developers regretted adding it to the game because of the issues it caused, but since it's part of the game now they weren't sure how to fix it without pissing people off. Same with flying, as they've constantly been trying to address the issues they see around the system. There's many more that have popped up over time and are still a problem but the players may be split over how to deal with them.
I recall an interview that Blizz did many years ago where they basically talked about how they felt if they didn't change the game (effectively what you call the paradigm) over time, the game would eventually die or at least drive many players away. In many respects, Blizz recognized the overarching pattern but hasn't really addressed or recognized what parts of the game are driving it in relation to their players. Part of it is likely due to stubborness, but another part is likely they're worried about fixing it because there will be short term pain for achieving long term gain. For example, if you add a system or feature that gets players addicted to it despite how much it's destroying their experience, of course taking it away is going to be painful even if it may be necessary. It's akin to someone being addicted to deadly drugs that are going to kill them, but waffling about whether or not to get them treatment because it's probably going to suck for them in the short term and get them mad at you. Even more broadly beyond a system or feature, changing how the game fundamentally works can be just as scary, and that's unfortunately what will be required to turn things around with WoW.
Many of the changes that have been proposed since 9.1.5 and into Dragonflight are nice and going in a positive direction, but it's still analogous to treating the symptoms and not the disease. The game has fundamentally broken aspects that are either a product of the changes Blizz made themselves or the changing player base of the game. A case can be made that Blizz is partly responsible for the player base they have, either by creating a game that fosters players to expect/behave certains ways or by driving players away due to their actions over time.
Still, there are aspects beyond Blizz's control when it comes to the players, but that's not an excuse to just throw your hands up and say "Nothing is broken, everything is fine, move along!" Many of Blizz's actions over the past expansions (even in Legion) were made with the intent of short term gain or maintaining the status quo with a long term damaging effect. Eventually the pain will be felt, and we're probably at a point where Blizz is starting to see that... hence the 180 degree shift in some of their policies as of late that shockingly seem to line up with a lot of changes players have been telling them were issues for years. However, I have to stress that many of these changes are very surface level with no real change in their fundamental design policies that are the source of the issues. Basically, the problems will keep coming back because the source issue isn't address or Blizz will still use broken philosophies to create more problems with the same source issue.
Overall, a paradigm shift needs to occur for the long term health of the game, and even Blizz has openly recognized this. However, they're either worried or stubborn about making such a change because change itself is scary. Be that as it may, change needs to come or the game will effectively die when it doesn't have to.