Are you sure you don't have jetways ? Jetways, at least in the default scenery, do not appear at all Scenery Complexity settings, so there might be a jetway even if you don't see it.
To check if there's a jetway, you can use the "Customize airport positions" menu options, which will list all parkings that have a jetway.
And, GSX will also say "Remember to activate the jetway" so, if you see this message, but not the jetway, it means your Scenery Complexity settings are too low for that one to be visible.