> No one is saying you shouldn't take the occasional walk while maintaining physical separation, in fact, that's what's being encouraged here.
It depends where. There are countries on lockdown where you are not allowed to go more than 100 m from your home even for exercise. If you live on a street consisting of blocks, then that means there are so many people at a time who would want to do their exercise, that you couldn't really maintain physical separation. Consequently, the authorities expect everyone to stay at home and e.g. buy an exercise bike. Also note that China’s approach in Wuhan was that no one may leave their housing block.
It depends where. There are countries on lockdown where you are not allowed to go more than 100 m from your home even for exercise. If you live on a street consisting of blocks, then that means there are so many people at a time who would want to do their exercise, that you couldn't really maintain physical separation. Consequently, the authorities expect everyone to stay at home and e.g. buy an exercise bike. Also note that China’s approach in Wuhan was that no one may leave their housing block.