I believe blizz just felt overly strong irrespective of activision and believe people will play with the game regardless. You never wanna blame for the company who had a big role in your childhood (Halo for Bungie and Warcraft/Starcraft/diablo for Blizzard) however acti. Still has good games that people enjoy.
I don't know if I'd point to any one major"thing", although obviously the Activision mix is one of the gold wow classic largest ones. However, I think you are correct in they became complacent and forgot what made them so popular to start with. Look at Diablo 3's launch, the lead guy working on it'd open disdain for the prior director, there was this arrogant feeling to the whole layout and release which everyone would play it just depending on the name.It's a pity, but it's the character of the matches business too. Companies come and go for all sorts of factors. Blizzard will sort itself out or fade off.
Idk Ive played because vanilla and people bitched about blizzard and wow sucking then to, I recall people HATED wotlk.If there's something that's been consistent regarding wow forms from 2004 to today is nonstop complaining and raging.The two things I hated about WOTLK was the return of Naxx and the Argent tourney. Especially since it was the very first raid after falling cash for the Xpac. Along with also the buy wow classic gold argent tourney had the strangest dailies ever and then a"raid" which you sat in 1 shitty appearing dirt floored space for 90 percent of it. Before falling into a pit and fighting a (edit) rehashed lvl 74 dungeon boss again...I think having Naxx was fine.
However, it being the first thing you encounter was only kinda meh timing. But anyhow they made up for it using Ulduar.Ulduar was the best raid Blizzard ever produced and it had been quickly made irrelevant from the worst raid Blizzard ever made. It's mind boggling.