And the whole fun of ARAM is that you get a random roll game.
Guess what. ARURF is NOT URF. It is a game mode based on URF and ARAM's love child. It isn't what you want, but you will deal with what you get. Should we only have URF because that is all Y player wants? No variance, no difference, because some people want to exclusively play a specific thing?
Maybe for the people who only play like 5-10 champions, then yes, ARURF isn't for them. For those of us who have a broad, deep champion pool, who enjoy playing just about every champion they own (All but like 10 of them btw for me. I will happily play anything, and ARAM gives me that random so that I don't have to pick between A, B, C, D... X, Y, Z, AA, AB, AC, ect.), this is pretty close to what we want.