I often come across posts where people are discussing the logic of a movie or comic book. An example could be Star Wars, where they discuss how a light saber works. Or which superheroes would win in a fight against each other. To me, it seems pointless to discuss such things as it is fiction. Just an insight into someone else’s imagination.
As others said, it’s fun.
Also, it engages critical thinking. One has to examine, make a claim, and defend with evidence. It may be silly, but it’s fundamentally helping you to think better.