A lot of the myth takes place in the city-state of Thebes, a place where all kinds awful things happened according to legend. It's the place where Oedipus gouged his eyes out, the brothers Polyneices and Eteocles killed each other, and Antigone hanged herself while buried alive. (Tough town.) After the story of Thebes' founding by Cadmus, this is one of the oldest myths associated with the city. We wonder if the Thebans had an inkling that their city was in for a ton of woe, when awful things like Agave marching in with Pentheus' head on a stick happened so early in their history.
There's a whole mountain range called Cithaeron just south of Thebes. (Yup, both are still around these days.) These mountains were thought to be particularly sacred to Dionysus, so it's no wonder that the myth says the god drives all his newly recruited Maenads up these slopes to partake in his Bacchanal. The mountain WILDerness of Cithaeron seems like the perfect place to have a WILD Bacchanal. By going out into nature, the followers of Dionysus can shed all the laws of the human city of Thebes and get down with their primal animal selves. You can even say that the contrast between Thebes and Cithaeron represents the warring nature of all human beings.