Because: cat like claws mean cat like infections.
Fishers round here are known for day time hunting. Very rarely do any bears in our area pose a danger. They're fairly docile actually, often run off soon as they hear you.
Bears have claws too. They too kill other critters to eat.
Every Fisher I've seen has wanted nothing to do with me, but I've had bear stalk me when I was turkey hunting, as he thought I was a turkey.
Every wild animal has the potential to carry some sort of bad stuff, a Fisher is no more of a threat then a barn cat.