I'm not a lawyer so I don't know if they could even file a Lawsuit, there are some "fair use" clauses in those copy right laws.
However they sure as heck wouldn't want to file a Lawsuit. those aren't just any sides or even a competitive product, those are speifically League of Legends Sites.
They are sides directly related to the actual product and they are even supported by Riot itself. They are pretty much part of the game and enhance it.
They don't take anything from Riot, quite the opposide, they add to the game experience and probably increase the amount of players the game retains.