GSX doesn't know anything about "how close" a stand is to a terminal, it doesn't know anything about the airport buildings, the only thing it "sees" is the scenery AFCAD and ( if you have one ) a GSX profile for that airport.
If the GSX profile for that airport has been altered to set the option to disable the passenger Bus, no Bus will come ( that's what the option does ), and if there's no Bus, no passengers will come either.
This is entirely normal, because right now GSX doesn't support passengers walking directly to a terminal, it's will be a fairly complex update that will also require a fairly long customization work in GSX, since for each parking stand you'll have to edit the path the passengers will take to the terminal entry, which cannot be calculated automatically, since there's no such thing as a "entry terminal door" in the scenery specification, so it must be made manually, for each gate. We already have all the capabilities in GSX to have passenger walking everywhere, which we shown in both O'Hare and Basel, where passengers walk around terminals and even climb stairs, so it wouldn't be difficult to have them in GSX too ( in fact, it's GSX that is creating those at KORD/LFSB ), it's just their path cannot be calculated automatically, not without having users complain passengers took strange path, walking into objects, jetways or vehicles so, the only option that would really work is to create those paths manually for each gate at each airport, which is a huge task.
So, right now, we just have the option to disable the Bus, which you maybe used thinking it would automatically cause passengers to walk to the terminal, but the only thing it does right now, is to disable the Bus, which will in turn disable passengers.
