when is urf returning?

Hi, I just installed league of last night and played a round of urf with my roommate. He went to bed and I played one more round by myself. Got up this morning and saw that Urf was no longer an option to play. My question is why they take it away in the first place and not just leave it up all the time? And secondly when is it coming back? Because I've been looking around to see if there is an expected date of return, but I haven't seen anything yet.