Doom: The Dark Ages has no multiplayer: 'Our campaigns are, to a great extent, what people come to the modern Doom games to play'
But it was also a very different world then, one without the countless assortment of multiplayer shooter options we can choose from today. So while it's a little surprising as a matter of principle (or perhaps just nostalgia) that Doom: The Dark Ages doesn't have any multiplayer at all, it's also understandable.