The reason URF will never be a permanent game mode

URF is it's own greatest demon. It's too fun, plain and simple. It distracts from the 5v5 riot wants everyone to idolize, to go pro in, to watch competitively, to start fantasy league teams over.

Or they could be like the McRib. It comes around to get a bit of a money boost for the company and then goes away before people can get sick of it. URF comes, league gets more people online that might not be as active from the basic 5v5 and the general Aram.

Think about it when URF comes no one really wants to do 5v5, ARAM's, and definitely not 3v3's.