In my primary school they did it based on the cleanest classroom. Except all we won was a $2 Freddo frog. The teachers wouldn’t let us vacuum though, and rather than just not eat inside and not make a mess, we went around with tape to pick up all the carpet crumbs
I think at the moment it’s mainly about causing drama and chaos. I’d say 70% are bots made just because we seem like easy targets, 25% are bots made by people with vested interested in the liked of Reddit and similar trying to cast doubt on the legitimacy of the fediverse, and 5% are just people making bots for no real reason