The only hackathons I've been part of were internal ones at a single job. Complete waste of time as the shit executives had already decided who the winners should be. So disheartening to see people deliberately misunderstanding our presentations so that they could vote for the team they wanted to win for political reasons. The final hackathon I did there ended with some execs saying "this is exactly how we will build software going forward" after my presentation.

Of course this was totally forgotten about mere hours after they said it.

I'm in the UK, so don't know what it's like elsewhere, but I get the impression it's pretty much the same thing.