game types being removed

I have an honest qustion, and if for some reason theres a simple answer by all means solve my confusion. I was wondering why game types like one for all, mirror games etc are always taken out, I understand theyre like promotional/holiday type events or what not, but still why can't we have these modes in custom? I'm bored of ranked at the moment, and blinds a bit stale too, but I love playing games where we can 5 man blitz or something retarded but funny, it usually gets me outta the lump i get into when I play too much league and dont wanna play anymore