Why Riot Games did not put 1 for all since like 2 years

Apparently it's to do with the voting process on the new client, It doesn't work and they've been trying to fix it, Hexakill doesn't work either, presumably because of the whole 6 champs during selection.

Both modes are greatly missed. Hope you are doing well on it Riot.

I think I read somewhere that it's needs some work to function with the new client, but they're working on it.