Riot Is Sneaky
I have the weirdest suspicion...that riot knows who the trolls are, but they dont ban them because they want the trolls to spend all their money in the game first. Then after a year or two, they ban a huge wave of players, pocketing the cash and wiping the trolls off of the game. Wouldn't be such a bad strategy for making money, but shows that riot might care more about money than dealing with problems that us good players face every day.
Of course they will ban or punish the occasional troll to make it look like they try, but in reality these trolls are getting fooled into buying stuff and then getting permabanned, never to access it again. [slayer-jinx-wink]