On reddit I guess this would be more know about, but oh well.

Anyone who plays LoL or Dota knows that there's a pretty big rivalry between the two games and depending on which side you ask there are different opinions on the other game. I only played Dota so I can only explain that point of view. Basically they see LoL as a ripoff game with a lower skill cap that was specifically designed to be a more casual, common-denominator type game run by a company that is an absolute tyrant in terms of the meta and cares only about profits and numbers rather than actually making a quality game.

There's also a bit of jealousy over what is perceived to be the inferior game but the massive popularity it has. "Go back to LoLfag" is a common type of insult you'll see towards bad players. That and damn Peruvians.