High skill cap champions are not worth learning in low elo
Why bother with Yasuo when you can pick Yi, go Q Q Q and get a pentakill for your team once you hit late game because your opponents didn't pick a champion with hard CC.
Why pick any bruiser when there's Darius who can win any melee matchup, has a broken ultimate, and is only slightly harder than Garen.
Why play another Mage in mid when there's Cho'gath. He can tank, sustain, burst, silence + slow, do true damage on his ultimate and be nearly impossible to kill without getting focused.