It was banned due to lack of targeted animal control, the death of numerous non-target animals including mammals, birds and fish and the slow rate of death to the hogs.
And, was proven ineffective due to that last one. Once a hog got sick from a non-lethal dose and recovered, they would never visit the bait site again. And, due to their intelligence and social hierarchy, the others quickly learned to avoid the bait from the one.

It was tested extensively in TX as well as here in AL.

And, I am sure there is something else being developed and tested again now.