Is there any way to exploit the ground network of an airport? I don't see its use seeing as its ORS is basically 0
well, it is basically a free of charge feeder or connection to any of your flights, respectively. pax do use it, however, as you already pointed out, it is very unattractive, so most likely, a lot of pax will pick choose a connection with a way better ORS rating. keep in mind, that the use of the ground network counts as one leg towards the maximum number of legs an AS pax takes.
.... and the AS pax will use the ground-network only to start or to finish a journey. NOT for transfer between big airports (i.e. London or New York).
Does it also work for cargo?
Yes, it works for pax and cargo.