Imagine the economic decision on that one?
Run a shuttle service that costs something like $500 per day, to be largely underutilized and even then mostly used by passengers who visit a lounge that gets charged to UA at another $50 per visit. I'm sure they're incentivized to offer this great feature! Hah.
It's about .90 mile each way in my Fitbit.
Maybe not a shuttle but conveyor belts for long stretches might help.