given their apparent absurd capabilities (eats anything, breeds like rabbit, grows to absurd sizes) I'm not clear what stops them from overrunning any environment they exist in, including their native environments in europe?

All of the natural predators coming up from googling seem to be fairly "weak" at population control -- alligators, cats, large birds (preying on the young) -- so it seems to be the wild hog has both the traits of an apex omnivore, but also comical rates of breeding; combined with their ability to eat just about anything (including each other), it almost as if the inevitable outcome should have been complete and total domination of the world centuries ago