Its nostr inherent but its the lack of a regular username or password. For diehard nostr users that is fine but for an online forum we need things like being able to assign moderators (even to specific subforums or threads) as well as other forms of login which then translate to a nostr account. Wisp does that with a google account.
And for private forums how does it stay private so that only members of that private section can see it?
Just a bunch to think about.