honestly i hate when addons are private and never released because the creator has stopped playing and providing it to the public. if anything, really cool addons that can help old and new coders alike go through and reverse engineer or take example from a previously built addon. not only that, the community doesn't loose really cool stuff.
while someone's add-ons are THEIR addons and are definitely entitled to have it to themselves, a courteous thing to do would be to release it if they plan on leaving the community or dont have fun coding with the addon as much as they used to. that would be mega rad