My friends are both pretty darn good software engineers, and went to pick up some other floaters to build a team there. They got a project manager, who they tasked with finding them more engineers. Project manager comes back.... with 2 more project managers. So with their team of 2 engineers and 3 project managers they got very little product done.
I think events like this shouldn't be called "Hackathons." Maybe "Pitch Events" or something. If you can win without writing a single line of code (which I have seen at two SF "hackathons") it should not be a hackathon.
Why? Just ignore the PM and get work done, just like normal.
PMs are great at hackathons for getting your drinks, talking to other teams, talking to judges and organisers about stuff they are looking for, getting the presentation ready.
So really the problem is the 3 other people on their team were just straight up incompetent / unmotivated, not so much that they were of X_Y_Z career.
Most of the teams came with something pre-made and tried to fit it to the theme of the event. And one team was pitching their startup. Of course all of them were good at pitching, but implementation-wise they were ahead of "hackers" too even not touching their keyboards...