Why can't URF stay? Because all these rank obsessed neckbeards enable riot to not care about fun. They scoff at featured game modes saying they lose their luster or whatever dribble they spout, so riot listens and creates cool game modes but just locks them all away because everyone is so worried about splitting the player base or some bs excuse. So what about TT, Dom, and ARAM? Those sure aren't splitting the player base like everyone thinks, there's a subset of people who play those modes, and they can enjoy it all the time, so it's completely ignorant for riot to string players along who don't care about the drudgery of ranked with a little taste of fun every few months.
My advice is check out Smite, that game has a variety of game modes including a rotation of different gimmick modes, one of which is like URF. This community is too populated by people who think fun is treating a game like a 9-5 job for riot to get any sort of perspective on how an actual fun game should be.