I had a similar experience several years ago with the shuttle bus service between an LA Metro Green Line station and LAX. They had 2 buses running a loop, which I estimated should take about 30 minutes. Therefore, when I arrived on a flight, I expected to wait no more than about 15 minutes. But the actual wait was 50 minutes! When we arrived at the Green Line station, the other bus was sitting waiting for passengers to come off the train.

This was in the late afternoon, when there were very few departing air passengers but lots of arriving passengers! The shuttle also carries many air terminal workers like retail and food service, but it apparently wasn't time for their shift change. So the stupid drivers sits at the rail station waiting for riders that never come, while other riders are standing at the curb at the airport waiting to be picked up.

The ARTIC situation might be similar.