Greed

Even Avalon barely has any information about the alien race that were together with the Empire aside from the information they have that was given by the Fyoran Race.

After all, the Galactic Federation didn't really wage war against the other race... When the Fyorans moved to the territory of the Federation, the Khrusams no longer attacked and decided to just ally with the Empire to have an opportunity once they got into a huge war...

At the very least, the Khrusam Race still knows that it needed to respect the power of the Federation. 

The extremely advanced technology of humans was something that they could not easily imitate... Aside from that, the adaptability and resourcefulness of the humans was also something to be noted since many of the alien races' technology that went into their hands became even more powerful once they decided to use them to their advantage.