Why no Episode 3 ???

[Kedjane]

Black Plague kinda is the end of it. They didn't leave a lot of turning room for additional plot either as the outbreak isn't until a month or something before Philip arrives. Everything before the outbreak is pretty normal and wouldn't work as anything but a novel.
They could make more story about the Archaic, but then it likely wouldn't have any connection to Howard, Philip, the Tuurngait or the Shelter.