[Kalzazz]

There big and look cool, and there cannon fire is cool looking, and you can put them in parades? They also are very cheap (they cost 350k in High Tech, through the miracles of plotholes and pixie dust, UT TL T72 knockoffs are magically assumed to be much cheaper)

They also are moderately resistant to small arms fire, and if the enemies are kind enough to attack their bow, moderately resistant to things which are bigger, and even at UT TL there weapons can still have some effect

Militias are not expected to be able to stand up against a full fledged invasion force, but, it is hoped that local militias can make an enemy decide to attack someone else, or failing that die slowly enough to buy time for assistance to arrive