This seems interesting. Any specific reason why it's over emails instead of something like a forum or discord?
Discord would be unpleasant for something like this with so many participants. It's a similar reason to skipping out on Hangouts, Zoom, etc. It forces synchronization, if you're not online during the discussion you're effectively barred from it. It can be very hard to catch up and very hard to respond to any particular thread of discussion. Discord is also, by design, essentially single-threaded. You can reply to spe…
Only a minority actively participates. But it's for all the other reasons you mention yes.
And, unrelatedly, even though few actively participate that isn't the point. It is a motivational vehicle. And I repeatedly hear about this from folks who join and don't participate. That's perfectly fine with me.