There are lots of poisons toxic to canids. Problem is USDA has to find one that, along with a delivery device if necessary, isolates the species for approval and registration. They also have to test humaneness and speed of lethality, cost effectiveness, etc.

And...

Most importantly...

political acceptability.

Yeah, I know, makes you want to puke, doesn't it.

Humaneness a factor for killing the most INhumane killers in the woods??

Good grief...