The reason a lot of champions get unwarranted popularity is that they have one or more mechanics or skills that are unbalanced. Sometimes Riot nerfs champions a bit too much, but would you rather have it where literally everyone uses your favorite champion because it really is overpowered and runs away to the next overpowered champion when it is balanced?
It happened to Olaf, it happened to Jax, it happened to Kayle, it happened to Kassadin. I'll agree that some of them required nerfs, but the cancer Kassadin group moved to Kayle, so Kayle got nerfed. They then move to Akali, wherein she faces a nerf. Next we'll see an upvote in Syndra mains, who'll make people miserable with 80% banrates, an eventual nerf, and a move to the next mage.
But what I hate the most is the refusal to touch the laning strategies because some people get upset when they see Lee Sin carry bot lane with a support. Muh Meta, Muh clarity, Muh I didn't have to think prior to seeing this. Yes, League and any other MOBA should be a fairly casual game, but you shouldn't be a brain dead idiot coming into the game expecting nothing to change.