Here's a much more realistic and far more accurate picture of why people are leaving. The developers took a fucking base ball bat to the end game that was so god damn casual friendly in wrath and cata. They stopped making dungeons as content entirely (yes i know some of you got sick of running them but you aren't casual players), they shoved everybody at end game into raiding or raid content at any rate (which is not casual friendly at all), they gutted extremely popular reward systems (once again to shove players into raid content) and told people RNG was good they should love it (which they didn't), and to top it all off in 5.0 they asked people to grind the most ridiculously boring and obnoxious and (once again) not casual friendly content in the universe daily quests. They gutted the casual experience to give the game a more vanilla feel (and their tweets will explain this to you in no uncertain terms), to offer some players "more to do" (when they had lots to do in cataclysm just none of it had gear behind it so they avoided it) and at the same time began to offer increasingly less and less in each patch that had any casual appeal or hell just anything NEW ffs. OH YAY ANOTHER RAID... WGAF? WGAS? Yes casual players left. The game became less suited to them when it became more raid oriented then ever. That's where your subscriber loss is from.
Now you can make the argument and the case that maybe warcraft isn't for them and you can patronize all you want about it but don't act like it's some mystery and don't give the developers licence to continue to ignore the actual problems by pinning it on things that aren't rational or are largely irrelevant or are even flat out improvements to the game (i.e talent system).