BC is incredibly basic, so it’s far easier to play, especially to suck at, and still complete the content. I’ve watched a friend’s terrible casual guild fail to get AotC two tiers in a row now, and their player mentality as a whole is to never improve; same effort, same results.
I think Blizzard is just bad at teaching players to be better at the game, or the evolution of the classes and gameplay they’re involved with. I think it’s abhorrent that tanks in particular level up without even having the basic tools to hold aggro on enemies (except Monk, I think?). It feels like early ArcheAge all over when I make an alt. The ability level-up system alone is convoluted and immediately hides their effects once you gain them, and that’s god awful game design right there. Fast forward to 60, and there’s no teaching players how to be better. If they don’t have the mentality to ask or seek it out they will always languish in mediocrity and burden the people they play with in pushing content.