Seriously. What the fuck is this trend?

Probably just something trending on social media. Influencers no longer decide what to do themselves but are controlled by algorithms no one really understands. One week it's pranking your dog, next week it's christian songs in an airplane.

And why doesn’t the airline staff or other passengers do anything?

Staff is not being paid enough to fight 15 people at once. Other passengers don't want to be charged with assault.