I want to see some service vehicles prior to any request of services.
On landing, it's enough to select the parking as soon as you landed, and so all vehicles will be there when you arrive, but no service will start.
On departure, I can't see what benefit you would gain by having the parking prepared without starting any services, since you are normally supposed to *start* a service, when you start at a gate.
The reason why we don't prepare a parking automatically, just by starting there, was made to make it EASIER to use it together with AES, so users having both products would have an easier time deciding which one to use on each session, and we expected AES to be modified to do the same (right now, it does what you suggest, automatically).
Since this hasn't happened in more than 2 years, maybe we might add an option to have the parking automatically populated when starting a flight there.