building infrastucture was what allowed capitalism to initially take off the rail networks were pivotal to their transitions into world powers. In America it allowed a vast continent to be truly connected and for the entire impperial core it made it so coal and goods could be rapidly transported and used in industry.

Infrastructure of the imperial core is vastly important for the health of the empire. The Romans weren't building roads for kicks after all. Neoliberalism is in some ways destructive to capitalism's ability to compete on the world stage as it turns capitalism's consumption on the mechanisms of the state which are needed to enforce it's will. A bit like an ouroboros.

transport and energy infrastructure might not be directly part of the military industrial complex but ultimately what's bad for the industrial complex is bad for the military industrial complex. And a lack of infrastructure is not good for industry