I'd have thought if a world HAS a highport that it likely has sufficient trade being warehoused and brokered at the high port, rarely seeing a planet's surface. Also, not every shipment is getting delivered to the planet, I'd have thought. Aside from anything else, the destination may be a space habitation or a secondary world within the system. It would seem counterproductive to land that on a surface then lift it back out to orbit if there was an orbital delivery option, in most cases.
Free traders are an important part of servicing a trade hub, too... they might land on the Type-C to pick up freight to be delivered to the high port at the Type-A next door, and move on to the next job. The freight they delivered is loaded up into a serious cargo vessel to be transferred in bulk to another hub, where other Free Traders may be involved in final delivery from its highport to the surface of a nearby destination.