This is typical group mentality of youngsters. They do what they want to do because they think it's cool. It does not matter if it's bad for performance or dangerous.
It's very similar to kids not wearing stocking caps when it's below freezing. Most of the kids I coached would eventually don some kind of hat when it got that cold, but some would not. Now you know that it does not make sense to stand out in cold weather for 4-5 hours without a hat/cap. But they did it.
It's the same with flopping or lying down on the track after a race. It's grandstanding...that is all.