I also lost interest when MoP came out. I came back for brief periods a few times in the following expansions but found them to not be very enjoyable. It wasn’t until Legion that I started enjoying WoW content again. BFA I’ve enjoyed very much and it really got me back into the game… however I personally feel like the addition of the corruption system has made the game significantly less enjoyable.
Prior to corruption the community complained about titanforging being too dependent on RNG. It confuses me why Blizzard went down the path of making the game even more dependent on RNG by adding corruption effects in lieu of titanforging, and then on top of that adding obnoxious effects to it. If Blizzard were to decide to carry the corruption system into the next xpac I would most certainly lose interest in the game as I did in MoP.
I have high hopes for Shadowlands though and from what it sounds like corruption will not be a thing going forward.