Probably because you don't even need them.
No, they're completely optional, you don't need them. Nobody can get into any trouble because there is no legal requirements on any mods.
Yeah, mods aren't copyrighted, and you don't need permissions as I've stated before. The only "copyright" mods hold are the Curse forums 'poopoo we don't understand how copyright works poopoo' thing. (HINT: The fake copyrights Curse forums requires modders to put on their mods is meaningless, since it isn't a real copyright.)