Why is custom URF disabled?

With (AR)URF live these past few days, I was a tad disappointed that I wouldn't be able to try some champs I was hoping to test for the past few months without getting a lucky roll. But I figured I could still fire off some custom 1v1s if it really came down to that. So after getting outclassed by people rolling their mains, and playing champs I'd bought years ago and never picked up since, I came looking for that reprieve.

Be it a bug or some questionable decision, customs weren't an option, despite it being active every past URF rotation.

With ARURF getting mixed feedback by the community, wouldn't it be a good idea to at least give us a choice on whether to play randoms or blind via custom matches?

Edit: Here's the link to the red post about the bug. Having urf released on time with one relevant aspect missing wasn't great, but it's understandable. http://boards.na.leagueoflegends.com/en/c/gameplay-balance/VpQIYfVz-arurf-custom-games-disabled-due-to-bug