The truth is it's the culture at FedEx. It's ingrained in the drivers psyche that they have to move like that at all times. They're constantly downtrodden and if they let up, it's worse.
On the City side they post your stops per hour from the previous day each morning and highlight your numbers. It's designed to publicly shame the drivers who under perform. They don't take into account what may have taken place on his route, only that he failed to meet the required minimum. FedEx believes people work best when working in fear. They like to discourage you from taking an actual lunch break as well. When delayed at a stop, the first thing they tell you is "switch your Intermec to lunch to get it out of the way" You see, we had to take lunch before the sixth hour. I could continue but you get the gist of the culture from these snippets.
I can't speak for all 367 service centers, but I can speak for Red's from first hand experience. It's not a friendly place to work.