Why do people cheer when a movie bombs?

Yes, it's a strange phenomenon.
I suppose some people enjoy thinking they can run the gamut of different streams of social media and perhaps even be instrumental to the failure of something they have some bias against (due to Director, Producer, actors or writer).

Or maybe some people just enjoy being negative and get off on the failure of others..It makes them feel better about themselves.

If a movie is part of a fad or trend that I don't like then I hope it fails so that there will be less of these types of these movies in the future.

It’s a lot of who side are you on too. Marvel vs DC or men vs women. Right now it’s popular to hate an all women’s cast or feminist type movie. I don’t remember the last time I heard a group of women hoping a macho man type movie to fail.

Those focused on the petty rivalry between brands/studios aside (being a part of it is tempting every now and then thanks to those looking for attention, I’ll admit), it’s everyone from film snobs to lifeless trolls and propagandists that live to hate on things because that’s how their fascistic selves are. Whether it’s this film or another big comic/action film with a so-called agenda, very agenda-driven detractors that cheer for the failure of movies/shows simply can’t let people enjoy things (some truly believe there’s nothing out there for them enjoy) and ultimately they find pleasure in pathetically rooting for the failure of a product that they decided they were going to hate from day one. It’s silly simple-minded individuals cheering - the toxic internet. Period.