The game has been more and more complicated and confusing over the years.
Back in Vanilla/TBC/Wrath, players used outside source/3rd party websites for talents, rotations, stats priority. And that’s it.
Even Elitist Jerks most crazy theory crafting days were not as ridiculous as today’s wowhead, icy-veins guides.
What players really hate about today’s systems is that they are unnecessarily over-complicated. Some says “you don’t need to do it if you just play it casually”. It may be the case back in pre-Legion days, but not anymore.
Today’s systems are so confusing and not self-explanatory, that most players can’t find any meaningful information in game. Even for the most casual players, it is just easier to check 3rd party guides for best pve/pvp talents, covenant, soulbinds, conduits, legendary, shard, and other millions of systems.
Systems were meant to be refreshing, meaningful and fun. But when they are so complicated and confusing, players will stop to care about them instead.
WoW has become a game of checking 3rd party website guides and sims.