I have to agree with Felipe.
The moving walkways ARE the main source of guest transport from the parking decks to CityWalk and then the parks. And while you specifically may be a casual guest that will never partake in any of CityWalk's offerings, from Universal's perspective, the current setup is a guaranteed money making machine. By literally forcing all guests to pass through their shopping and dining district, it exponentially increases the amount of guests that will decide to spend some dough.
So offering a means of transport directly to park gates, meaning less money going to the entertainment, retail, and dining options, would simply be a massive mistake for them financially.
And come on,
it's not that long of a walk from the end of the walkway bridge to either park entrance, considering the amount of walking a typical guest then has to do while in the parks themselves.