Commissars (Soviet era-type political commissars) typically exist to keep an army loyal to the state and indoctrinate them to the singular party of an authority's state. But with an army already loyal, they aren't all that useful in that role.
What could commissars do without this role?
This is for an entirely mechanised force. The government isn't authoritarian and is a functional democracy, although the military has a lot more autonomy than in most nations, and it's difficult for the government to force them to do something regarding their internal organisation. The government still determines where the military actually goes and what it does.