it is an apparent effort to concentrate the public decision-making power over matters of war and peace in particular – given the unique competences of this assembly – in the men who had served or who would serve in the military. I think this goes a long way to explaining why this assembly, but none of the others, so aggressively disenfranchises the poorest Romans.
If you can't afford arms, you can't serve, and if you can't serve, you can't vote.