Why can't Snowdown Showdown be a thing in Custom games?

There are so many occasions where my university likes to hold a 1v1 tournament among students, but having it done on Summoner's Rift with the host as the 3rd person to spectate our match carefully is just so awkward af.

I know Snowdown Showdown isn't a very popular mode which is why you never brought it back for so many years, but could you at least let it be enabled in Custom games anyway?