They probably do have nothing better to do, and that's a good thing. Basic queuing theory says that a system needs excess capacity in order to be able to respond to peak demand - you can't just tell a second fire to wait for an hour while fighting the first one. If three engines respond to a fender bender and a more pressing call comes in, they will leave and go there.

I had an immediate family member in the hospital when that "nurses playing cards" ignorance was going around. I wish nurses did have some time to play cards, because it would mean they'd answer when they were needed, rather than being busy with other patients for an hour and then forgetting. We truly are optimizing ourselves to death.