> The fact that mice don't appear to deliberately jump off high things as a way to get down tells me that they probably do get hurt...

They explicitly added the caveat about the soft ground. There'd be very little opportunity for mouses to become comfortable with jumping from high areas as there'd be very few occasions that satisfy the requirement. If the mouse jumped into a cave and can't get out, it'd starve to death. If it jumped off a cliff and fell into water, it would drown. If it fell off a skyscraper, there'd be Asphalt at the ground etc. Off the top of my head, there are no natural places in which mouses could safely get comfortable with jumping. Thus, they'd only do so if they're in mortal danger. And they absolutely do jump off high places if they're terrified