They do however not contain the taxiway and park position information GSX uses for its services. This is the reason why your GSX can't be used at these airports. As far as I know the developer has no plans to update this.
That's correct.
GSX needs at least two parking ( at least one for your plane, and one two spawn its vehicles from ) and they must be reachable with apron lines/taxiways. That's the bar minimum for GSX to operate at any airport.
If the scenery developer is not interested doing this, there's not much we can do.
I think I know why they are not added any parking taxiways: because they will never work very well, since FSX and P3D up to 4 didn't really supported sloped runways. However, P3D V5 has changed this and added support for sloped runway and taxiways so, if I was the designed of an airport that has being sloped of of its main points of interest, I would immediately jump to the chance to make a proper version for P3D V5, which would allow AI to go there too, not "just" GSX.