It is viable for a race to take place at the same time as a marathon. From a logistics point of view, there is benefit in trying to draw in both those interested in marathons and those interested in racing. But there is a difference in motivation. Choose at random one of the 70,000 registrants of the NYC Marathon and ask them if they plan to win: the answer will almost certainly be no. They are there to see how far they can push themselves only. Whereas in an event that is strictly conducted as a race, generally every participant will tell you that they are seeking the win.

It is also viable for a sales pitch competition to take place at the same time as a hackathon. When we look past the early hackathon days, we can observe a trend towards events hosting both. Similar to marathon/races, appealing to a wider audience helps with logistics. Maybe that is where things get confusing?

Perhaps this is easier for you to reason about with a telethon? Rarely do we find a competitive element show up as being an objective of the event in that setting. Only the endurance component, where telephone operators push themselves to answer phones for periods of time beyond what would be considered normal.