It probably helps that the worms don't care. That is, a worm whose ancestors lived in dogs can live in a human no problem and vice versa.

If you eradicate GWD in your region but, eh, not in dogs, well people in your region keep getting GWD anyway. But if you eliminate it entirely you're just done. So that's a strong incentive to ensure the latter.

Most drastic options are probably available in the afflicted countries than would be acceptable in many places that haven't had GWD for a hundred years or more. If you tell the population of rural France that military and police are going to start shooting wild animals dead as a disease control measure there will be mass protests. But in South Sudan hey, at least you aren't proposing to shoot all the members of some minority ethnic group.