The reason why I think jungle is the least desired role
As a previous gold player last season I was terrified of the jungle (never jungled before) Reason? The game does NOT encourage you to go before you have a full rune page AND the usual mastery of a champion. I did not "Grow" up with learning how to jungle. The additional difficulty of what was the optimal route of the jungle also made it scary. Lanes are at LEAST 3x as easy as junging. This season I am trying to get into jungling by trying warwick but I STILL do not know the route I'm supposed to go. That is how bad jungle is.
Another reason is that people blame you if you either gank without a kill, gank and die, or not gank at all, and failing to smite the dragon or baron and possibly costing the game.