Why does Riot do this? (Clarification question)

According to everyone, Riot said that they can't use our skins and champion concepts, or even our lore ideas, for what I assume would be "stealing" other's ideas (I haven't actually seen anything from Riot about it, just a lot of comments). So my question is, why does Riot even have this system, a way to show off and give potentially great ideas for skins / lore, if they can't use it?

Again, I have only seen comments on this, so I'm just asking as clarification.