You don't abandon them, you deploy them as a tactical element, use them on-planet to reposition forces as needed for the duration of the operation, and then take them with you to the next planet to invade. If not, then you've got to build replacements for them for every world where you fight. The factories may build extras for use by the planetary militias after the SLDF forces leave, but the ones brought by the SLDF would almost certainly leave with them.
The majority of the landing forces would arrive in system on the Warships, some on the accompanying larger dropships, and would be ferried within the system from the Warships to the planet aboard those dropships. The smaller Leopard and Confederate class dropships would mostly be dedicated to operating in close cooperation with the forces on the ground.
Additional supply dropships would follow later, using civilian-type dropships, in sufficient numbers to support a planetary invasion with food, ammo, spare parts, and reinforcements as needed. With the Warships being priority targets, and almost all lost during the Succession Wars, only those civilian jumpships and various dropship types remain.