The dragon kin bodies started from Warrior Princesses. Noble and strong, keen of intellect. Usually princesses that had directly contacted the dragons to save other women sent off as tribute.
These dragons had no taste for sentient beings, but many humans were confused on that point. Sometimes sending a young woman to dragon enclaves.
They offered the noble warrior princesses a deal: "Leave your bodies behind, and your soul can travel the galaxy for unobtainable adventures beyond the stars."
The dragon kin used the empty bodies. Dragon souls within human form.
Accepting conditions from each of the donors, which added together, meant: "No inhuman children should be born. The husbands should be equal to our Warrior-King fathers."
This is the core of the problem for the dragon kin. The humans of that planet have become focused on Science, Technology, Engineering, and Math.
Gone are the empires of warrior kings.