If you piss off enough mod makers, they never will be. I've tried making a mod before, its tedious and time consuming. I'd be damned if I spent personal time on something, gave it to a community for free, then had some dude rip it in order to make a one year later mod without asking permission and/or giving credit.
I can't speak for mod makers, but to me it doesn't seem like an "ownership" or "IP" issue. Its a common respect issue.