Hilarious how the Blizzard dicksucking sites turn off all their comments on posts about the ongoing sanitization of WoW. Can't let the pesky little peons have a voice, no sirree!
Everyone started somewhere on the slope, but for that person, that's the peak.
There's truth to that, but looking back, the biggest reason why the "good" expansions felt less good each time was the loss of a personal community.
When I started in Wrath, one of my best friends from high school got me into the game, invited me to his guild, and brought me through my first raids. Long nights hanging out on Vent, shooting the shit and having a good time, laughing at our resident Mexican anytime he got ridiculously angry (which was all the time). Then Cata hit, the guild started to break apart, and even my friend quit playing. Only a core remained, but as soon as the rogue got the legendary daggers, she and a few others bounced servers, the GM fled for greener pastures, and I was left alone.
In Mists I tried again with a fresh guild, and we had a decent go of it, but for the life of me I really don't remember anyone in there except the GM (who was a really nice guy, hope he's doing alright). There just wasn't that same connection, and people went their separate ways before the first raid tier was over. I managed to get the GM to transfer the guild to me, and I used it with another friend group for a while, playing casually. But eventually they stopped playing too, and so I ended up alone again.
I didn't even bother trying to reform the guild afterward; I've never been guild leadership material, and I just didn't know how to go about recruiting people. I had no desire to get back into progression raiding, and pretty much anything I cared to do could be done by myself or in a pug. So I played the next two expansions by myself, and even if I liked a fair amount of Legion's content, in retrospect I can see how much I was missing having people to play with. When BfA flopped out of the starting gate, there was no one keeping me tied down and no reason to stay, so it ended up an easy decision to quit.
You can extend this argument to server communities and such, but it's more about the personal level to me. You
can play WoW like a single-player RPG, but it's just not as much fun without friends to play with.