Risk in crossing the street, but that is not at all relevant. It is about minimizing unnecessary risks. Every time a football player enters the field of play there is an x% chance of injury. When a game matters you take that risk every time. But when it is essentially a pointless exhibition you don't take the risk. It is simple risk/reward logic. There is a risk, and no reward, easy choice. If they come out healthy it only cost them a day of rest (which isn't zero at this point in the season). But if they add any injuries that is entirely on the coach and his silly bravado.