The law may be on the side of CBS and Paramount, but I'd like to know how they're harmed by the production of fan fiction. There's a case to be made that use of trademarks may be a problem, but the companies chose not to pursue that issue. They focused on copyright. How did this harm them?
Fan fiction doesn't reduce fan interest in the franchise and the works created by CBS and Paramount. Instead, it increases interest, by keeping fans interested in between series and movies and perhaps winning over new fans who might encounter the videos on Youtube. Thefan works are non-canon, and there's no reason why it would reduce the desire of fans for films that are considered canon. For example, Star Trek Continues makes use of most of the TOS characters played by different actors. I don't see any logical reason that Star Trek Continues would reduce interest in TOS, though. If anything, encountering that on Youtube might make viewers want to watch TOS and increase revenue for CBS and Paramount.
How could there be any damages to CBS and Paramount? Those donations are to cover the cost of production, not for the creators to pocket the money. That money was never going to CBS and Paramount anyway, who don't solicit donations to pay for the cost of their films. Instead, the studios set a budget, invest that money, and get paid though advertising and at the box office (for movies).
How were CBS and Paramount possibly harmed? And if they're not harmed, how could they collect any damages at all?
Source : https://yro.slashdot.org/story/17/01/21/000249/cbs-paramount-settle-lawsuit-over-star-trek-fan-film