Public Transportation: Why are MOST bus drivers so bitter?

Let it be known out of the gates, I'm not calling out every bus driver, just most of them and they know who they are. I've been indulging in the public transportation thing now that I have returned to school and find that most of the bus drivers for BAT (Bend Area Transit) have more attitude than 12 high school sophomores. It's like they are reluctantly letting you board their personal vehicles. Alot of sneers, frowns, and just plain p*ssed-off looks. They call the stops as if they were commanding you to get out of their hair and get the hell off their bus. What's up with all this attitude? Shouldn't they be happy they have a job? A secure job no less. Granted, I have met some friendly drivers who are a pleasure to ride with but the majority seem to have a stick inappropriately placed in the middle of their bus-driver seat and they want you to experience the misery they are feeling. I've been around and have done several jobs in which driving "precious cargo" to and from has been part of the gig. I have never felt the angst and/or rage these drivers seem to have bottled up inside. Did I miss something? I will continue to ride and enjoy the happier drivers but I will continue to be baffled by the drivers that make you feel like they are going out of their way to drive you to the place that they are already going to anyway. Just one of those things that make me go "Hmmmmm???"