The apocalyptic cataclysm that was the Fall of the Old Zu'Aan Empire destroyed a lot of the infrastructure and with the extent and methods used, the the biosphere was damaged and this means billions was affected planet-wide. There was a nuclear winter that lasted for months at least, perhaps even years (which is enough time to cause a mass extinction event on the planet depending on how many bombs detonated). Because of that is the case, with the nuclear war destroying much of the infrastructure and the remainder being covered in radiation, then the technology is lost, initially the infrastructure required to make it and later the knowledge as generations pass since the exchange.
The technological stagnation was in part due to a lack of efficient education systems and sheer amounts of technophobia, in both the Zu'aan and Vampyre races.
Galas Malatar Project