Why Lee Sin is literally Riot's child....

Because like alot of "good parents" they have a child that can be nice, and sweet. And a pleasure to be around, fun to have around. But, he can also get into trouble and mischief. He steals sometimes. He tells a few lies. And sometimes he hits people when he's upset. But, Riot won't ever nerf or balance Lee Sin, because they love him too much and are too afraid of losing his love and appeal. Compared to Riot not wanting a giant backlash from the community. It's like refusing to dicipline your child because you're trying to be their friend. Be their parent.

Lee has always been problamatic. He just happens to be the favorite child, and until Riot matures are "parents" their child is going to continue to be a toxic member of the community.