who's the ''brilliant'' Rioter that decided to remove RGM for season 8?

Every time they run a RGM, they can't just "turn it on". They have to do testing, for bugs every patch, and they need to make sure they arn't super buggy in the gamemode they are pushing out. For example, Zoe had some bugs on her w, when they were testing her out, they noticed that on one for all, that they could see the other zoe's w bubbles, but could not pick them up. so ya.

They are testing all for one so they can bring it back, and what Mango said, do you not read patch notes?