The Romulan Mortar Teams had hidden themselves all over the Abandoned Human Cities to ambush the Vulcan Infantry and buy time for their Reinforcements to land with the supplies they needed to build their own Combat Vehicles to stop the Humans from overwhelming them!

The Romulan Colony Hub was upgrading itself to the Improved Romulan Colony Hub and the Romulan Vehicle Yard was still being built while the resources are being beamed to them from the Romulan Starships fighting the Vulcans.

The Vulcans and the Romulans both had to import the same kind of resources from other Solar Systems to manufacture everything from, so both sides can steal supplies from crashed Starships while the Humans didn't have the resupply problems to deal with at all!