I'd really like to know why they DIDN'T consider something like Redis for this - if I'm thinking of my own apps where I just take redis==sessions for granted, w

I'd really like to know why they DIDN'T consider something like Redis for this - if I'm thinking of my own apps where I just take redis==sessions for granted, why would they make a technology change of this magnitude in order to cover a usecase like that? Maybe there was a lot more?