Forever ago, when I was a freshman in college, I read an essay about how authorities in some city discouraged vandalism. They knew certain young people were spending days spray painting huge murals but waited until the individuals finished the project before having someone paint over it. The young people weren’t charged or anything. Their “punishment” was having their art which they spent days on unceremoniously covered in plain white paint.
Point being, I can see Paramount or X company deterring unauthorized use of its IP by waiting until the fan film(s) is finished (or nearly finished) before dropping the cease and desist hammer. It may be shitty, but it’s kind of a good strategy. Occupy the creators of the fan film for years so they’re busy and can’t regroup to try again then kill it late in the game which may deter other people from trying in the future.
Then again, maybe these companies should pull a (specific) Sega. Christian Whitehead’s engine used for a fan game and porting old Sonic games to mobile was so good Sega was just like, “Fine, make us a real one.” And now, we have Sonic Mania.