Car Pool or Driving Fool?

The Antelope Valley freeway has car pool lanes. They are 'part time' lanes, meaning they are only limited to car pools during the busy hours. Last night I took my mom down to LAX (Los Angeles International Airport, for those not in the know about airport codes). Coming home I reached the section where the car pool lane is, and since it was well into off hours I was using it. When I got in it it was pretty much wide open, and even though I wasn't driving really fast I was going fast enough to appreciate the space.

At the very next access point I could see why I wanted to be in the car pool lane. The other two lanes were pretty well clogged. A guy in the left lane of the two was driving along at right about the speed limit. For anyone unfamiliar with California freeways, going the speed limit is not considered normal or courteous behavior, going the speed limit in the fast lane is downright rude. Anyway, I was fairly happy to be in the car pool lane and getting by the jam-up of people having to go around this guy on the right.

I was happy until at the last moment he swerved into the car pool lane! And with the mass of cars that had been stuck behind him still on my right I couldn't get out! So I followed this imbecile into the next 3 mile segment of the car pool lane. Anyone who knows me can well imagine the state of mind I was in after three miles of driving the speed limit on the freeway in the car pool lane at ten o'clock at night. Two lanes of traffic going by on the right, generally at speeds about twenty miles per hour faster than we were going did not improve my state of mind, nor did the ten cars backed up behind us in the car pool lane.

Can anyone explain to me what would make someone think that they needed to get further left when they were already being passed on the right by a multitude of cars? I wanted to ask the guy, but I was in a hurry to get home to my girlfriend, and she doesn't approve of me stopping people and asking them about their moronic behaviors anyway. She is afraid I would get in a fight.