I can imagine they make good bait. I’ve fished with the rubber versions, just never thought of it.
It is odd, I actually grew up near Frankfort, right on Lake Michigan. Ever go to Sleeping Bear Dunes or canoe the Platte River? I’ve spent a lot of time on the big lake and the inland lakes and rivers in that area, and I cannot recall once seeing a leech swimming anywhere. The only time I encountered one was in elementary school, someone brought a turtle that they caught to school, and a leech fell off of it. I then go live in the UP, and I go paddling in Manistique Lake, and they’re everywhere, just kind of wiggling by, trolling for some animal to stick to, and they’re several inches long too. All the other lakes were like that too.