The dudes they pick utilize poor strategy. They come out the gate hot, and are gassed by 50% of the race. Really, they should be running at a pace they can just barely maintain to the end, and then push all out the last 20m
I've run over two dozen marathons. Even at that distance, it takes a lot of discipline to not go out too fast. These are random people they find in the stands who are going to be very amped up in the moment. Strategy is the furthest thing from their minds and even if weren't, it takes practice to know what your ideal pace is.
There was a display at an airport I read about. Had a projector showing the average speed for a champion marathon runner. Most normal people couldn't match it over the short distance.
Couldn't find the link but here is a similar video of people (mostly amateur runners) trying to match a 2h marathon time for two minutes:
It takes a lot of practice and training to learn how to pace yourself in order to do that strategy. Some rando off the field isn't going to be able to do that. Hell, I think even experienced runners may have trouble doing that for distances that they don't run regularly (e.g. a 100m specialist doing a 800m or a marathoner doing a 100m or 400m).
