They didn't seem to have as much success with it back then. I wonder if we will find out it has more to do with the guts than blood and flesh. That did seem to be all guts smeared on michone.
I think they haven't used it more often because who wants to be perpetually coated in zombie goo. They used it in a very specific instance while in Atlanta, as did Michonne when she walked up to the fence. It's good for limited use, but wouldn't want it on me 24/7.