It doesn’t have much to do with whether or not they catch fish because everything I have used does that, it has only to do with how hardy they are. In my observation they just don’t stay active as long and once they are hit they are done, some other baits you can keep on using and they seem to last longer even after being hit. Believe me I use them probably 90% of the time I would just like some more options at times, especially when I am getting low on bait and want something to stay alive a while.
The other thing I don’t like about using bluegill is that they are persued by other anglers for sport and food and I like using the larger ones that they target. I rather use something like a baby carp or even drum that is a juvenile as opposed to an adult reproducing bluegill. Just a little conervation minded bait concern.
What I don’t like about bullheads is at times they can lay down and not be as active as I would like. Occasionally you have to pop the rod a little bit to get them moving again.
Sorry about the longish post, I just really love talking baits!