OMG he gets burst on his ult! OMG so much mobility with ward jump! Meanwhile Rengar and Kha'zix are able to burst you like every 2 seconds. And they have WAY more mobility than Lee Sin will ever have. Not to mention the fact that you ALWAYS know where he is.
hi im bannned1 voteswhat is your point...?
Dynikus1 votesPeople complain about kha'zix and rengar too, though, and both are banned more than lee.
Cloud2731 votesLee Sin is a healthy champ, as annoying as he is. We have much bigger cancer in this game that needs to be nerfed.
AFilthyCaitMain1 votesPeople seem to do the same thing to a lot of balanced champions. Eg: 
Big Lincoln1 votesboards is mage mains and mage mains hate when melee champs can reach them
Taliyah Rocks1 votesBecause he has lots of outplay potential. A good Lee Sin can out-maneuver you and kick you in his team. Also he has the best early invades, being able to jump over walls, gap-close to you from out of sight, and slow you to make sure your don't get away while having high burst and sustained damage. A good Lee Sin can shift the game really early. As a jungler main, if i start blue, there's ALWAYS a Lee Sin at my red (or vice-versa). I can't even ward to prevent the invade, as soon as i come into range of the bush to ward, Lee Sin just jumps on me.
He's really annoying and can snowball the early game so hard.
BUT!
The biggest issue... is that he's very polarized. If he fails at his job, he because so freakin' useless, that he's a deadweight to his team. I've come to hate both Lee Sin on my team and on the enemy team.
Plus his winrate is decent, which makes him a safe pick despite having such a huge impact on the game (wether positive or negative)