You’re quite hilarious if you think people just stuck around doing the same thing over and over again after clearing raids. But hey, you’e looking at an arbitrary graph and assuming you know why people left, without actually talking to those people, so not actually surprised.
The trend is right in front of you, look at the explosive growth of the MMO genre in the last ten years, we went from a handful of MMOs with WoW as king of the hill to several viable contenders. You can check out any mmo on the market (playing 4 different ones myself right now) and in all of them you’ll find people who come from WoW and play when content dries up in WoW.
I don’t need numbers to show the trend, it’s obvious to anyone paying attention. It’s obvious to any who bother to look at the number of companies investing in the genre, new IPs releasing like clockwork, new IPs being fleshed out to offer different experiences for different players to suit their playstyles.
But sure, let’s go with your argument.
As for people leaving when they get BiS, you really should pay more attention to the people around you, get out more, experience different games, different communities. Because your assumption that this isn’t a reason people dip from a game inbetween patches is absolutely hilarious.