Registered non-profit <> non-commercial.
- a private website for my local sailing club.
- a mod for a game
- an open source project that requires a private repository for a few things
- any project relating to a private community
None of these are registered non-profits.
Bitbucket is capped at 5 users as far as I can see, and self-hosting is just a recipe for lost data. I don't know of many amateur groups that can safely host a server.