There are a lot of things that, if done individually, make sense, but if the whole group does it there is a problem. Leaving your bag behind means that you have

There are a lot of things that, if done individually, make sense, but if the whole group does it there is a problem. Leaving your bag behind means that you have to replace it later which costs a lot and takes time. So it makes sense to avoid this trouble. It also makes sense to rush to wards the exit if there is a fire but if everyone does it you have a problem.