Quoting from the GSX Manual, Page 15:
Waiting times for vehicles like Catering, Bus or Refueling trucks
All GSX vehicles that comes from away, by default are spawned from other Parking spots of the “Vehicle” kind, with the Fuel Truck starting from the “Fuel” Parking types instead. They try to use taxiway paths of the “Vehicle” type, which in real life are also used to provide safe paths for service vehicles without affecting airplane traffic. The “vehicle” paths are given an higher weight in the pathfinding algorithm, so even if the route is longer, GSX vehicles will try to use the proper paths, if possible, and there’s no other route, they’ll use regular taxiways or even runways, when no other route is available to reach your parking spot. This might result in some waiting time, depending how the airport is made, large airports usually have several areas with many vehicle parking spots each, but airports in the MSFS world are not always well designed, when ground services are concerned.
Some GSX vehicles spawn from your parking spot, because in reality things like stairs or pushback trucks are stored very close to each parking spots.
However, other vehicles, like full baggage carts used during Boarding and Catering trucks, realistically come from other parking spots, because they are supposed to come from other buildings like the baggage handling or the catering facilities, so it would be wrong if they pop-up in front of you.
And of course, they should come from parking of the "Vehicle" kind, because, on a properly designed airport, these are connected to paths of the "Vehicle" kind, which would ensure a proper flow of ground service vehicles that won't clash with airplane traffic on real taxiways, that's why there are dedicated vehicle path in real world.
And that's why GSX assigns more importance to vehicle path, even if the route is longer, so its vehicles could stay away from airplane taxiways as long as possible.
The key here is "on a properly designed airport", because while in real life there are multiple clusters of dedicated parking zones for ground vehicles, and vehicle paths are many, that's not always the case with MSFS airports, which might not be designed with the same care for ground vehicles.