I think a good example of why 4chan jannies are so hated is when Billy Mitchell won his lawsuit several weeks ago. The rules of /v/ lay out that it is a board discussing video games and video game culture. Well, Billy Mitchell is clearly a major figure in video game culture, and this was a topic that a lot of people wanted to discuss. Jannies were patrolling the board deleting anything that looked like a Billy Mitchell thread, including OPs that were just about the Donkey Kong arcade game.
Now if the board was like 25% threads about Billy Mitchell and his lawsuit, then yes, of course you've got to clean some of those up, but just one thread about this topic that clearly a lot of people wanted to discuss isn't going to hurt anything. Especially considering how many threads are just dedicated to masturbating to fanart of video game characters, which there are other boards for.