I think it's a pretty well known fact that Lee Sin is no longer the very top tier jungler.
What about Vi and J4? To me they're 10x better than Lee Sin. Especially Vi.
Yes, Riot once said something about the Popularity of Lee Sin so they won't meaningfully nerf him, but there are better junglers out there now than him.
/end rant
Well, it could just be that these jungers are easier to play. After all, Lee sin has more difficult mechanics than J4 and Vi. Vi is like... pop ult to win, and J4... pretty much the same when they're ganking lane. Lee sin? You have to know how he works, and coordinate your skills, which, if done correctly may be on par with or even better than Vi or Jarvan. It's pretty often that a champion becomes less desirable because the learning curve is not worth it when you can get pretty good results with easier to use champions like J4 and Vi.
J4 and Vi players... don't get mad at me. I grossly oversimplified how to play J4 and Vi, and you can really tell when you have a player new to either champion, and they do take some skill, but my point is that Lee Sin has more complex mechanics at work.
It's because of how he is immune to nerfs because, according to Rito, he has a "high skillcap". Of course, Lee Sin isn't OP, but they way Rito treats him like a prince in terms of balance would definitely make the playerbase angry. So, there's gotta be some kind of tradeoff here and there. Sure, it's great to be left untouched by nerfs/buffs, but he's gotta take the blame of all those "muh #LCSBigPlays" and shit like that.
Meanwhile 
. Need I go on?
People like to complain about flashy champions. That's really all there is to it. Statistics suggest he is pretty sub-par.
