Why are invites tied so closely to private messages?

Why is generating invite links to join the forum tied to adding existing users to private messages?

We accidentally disabled our staff being able to add users to messages because we wanted to disable the “Invite” widget under user preferences since it serves no purpose on our forum. I’m not sure why these have to be tied together with the same settings – it’s not intuitive at all.

For me the expected behavior is that there should be a different setting guarding whether you can add people to private messages, separate from whether you can invite users to join the forum.