I don’t think this is a specific cultural thing, in my experience some people host more curated gathering, some more relaxed and informal - doesn’t matter where you’re from. People just tend to think the way their social group does it is the ‘norm’.

I think there's a cultural element to how much of it people will know to do without being explicitly told what to do.

In the US successful gatherings tend to require a fair bit of wrangling - I've been to more than one potluck where everyone showed up with roughly the same dish...