Why is a decade enough to make a game that would have probably taken 15m to make, then wait the decade?

Because not all games make fifteen minutes to make.
I have plenty of game stuff i've worked on and which were never released, but which i could probably release some day in the future. This jam is just a reminder to tell you that you should probably take your time :) you never rush a game for a good reason.

You can submit as many games as you'd like. I see this jam as an experiment to see what would happen with a long-term jam.

I think the better question is

why not?

Wynaut!