Kahn revealed to Omega that in just a short amount of time, the Great War with the Demon Empire would start and thus, he needed to have an entire army of his own; not just summoned subordinates he made from monsters and warrior class species, but actual living beings of Vantrea.
[Kid… how did you find that out? Even the Sovereign that brought you here doesn't know this. Otherwise, we would have been warned already.] inquired Rathnaar.
"It was the Hero of Time who babbled this when I fought him. He was from the future so he obviously knew much more than us." said Kahn as he put the whole blame on Anakin.
Obviously, he couldn't tell Rathnaar or anyone else about the changed timeline or some events of the future due to his promise to the Martial Emperor.
In the original timeline, the Martial Emperor aka future Kahn was still inside the Beast Empire, hiding his identity and met Argos Belmont only after it had been 2 years since the Conclave of Heroes.