Yeah 99% of copyright cases happen.because the law requires rights holders to act in their copyright's defense otherwise they lose claim to it. So EA sued that fan-made starwars game because copyright law requires them to pretend they care about. Copyright law doesn't require them to ever do anything about fan-made mods, so no company ever even pretends to care about mods.
Basically there's 0% chance of ever seeing a DMCA over a mod. The only way copyright applies to free mods is in respect to the work of fellow modder, you don't have to worry about EA
You are mixing up IP and Trademarks: it's the second one that has to be enforced to be kept valid. IP are enforced at the discretion of the rights' owner.
As for the "0%", well I can find dozens results with a simple search but for the sake of argument:
Battlestar Galactica mod for Nexus,
A couple of Mass Effect mods, (they are actually friendly to modders but you have to ask for permission first)
Starcraft World mod for Starcraft,
Several mods inspired by the Tolkien Universe,
In the past, several Warhammer mods (although now GW encourages them)...
So yeah, point in case: there are mod friendly IP owners, and there are others that will take down anything that blip on their radar.