Rampant botting
With NA being a region where Riot could hook a lot of big fish to drop money on the game you would think that they would want to get these bot farmers under control. New players that have money to spend are likely to take the large number of AI as a sign of a failing game. Given that most of Riots new projects tie heavily into league it will probably cost them a lot of potential sales in those properties as well. Just a though.