I like Jason Schreier's take that the end of Blizzard began as soon as WoW blew up in popularity.

"Imagine a Blizzard that never made or never found the success they did with WoW and continued on the path of boxed releases every couple years."

I did find myself rather salty back then that it felt like Blizzard abandoned anything outside of WoW until 2010. WoW wasn't something I ever grew an interest in, yet I played an absurd amount of SC and WC3. Then SC2 was a huge miss for me, as well as every game after it.