I can't think of another game that has nearly this level of complaints toward matchmaking. At some point, there is a problem with Riot's system and it isn't just people complaining. If Riot keeps thinking this, they will wake up one day and realize they missed the boat.
Well, it probably has to do with the fact that it is so widely played (THE most played online game ?)
Seriously, if you read the complains, you'll find out that : the matchmaking sucks, every hero is OP, every item is bad, the meta is stupid, Riot is the worst company ever, and players are 99% kids, trolls, and noobs.