Rant: I see this in the Bay Area all the time. On many freeways, the fast lane is also the carpool/HOV lane, at least during high-traffic times. The idea is that the government wants to encourage carpooling and/or low-emissions vehicles, therefore restricting the fast lane to such people would encourage such things.
But I often see people get in the fast lane not because they want to go faster than the adjacent lane, but rather because they have more than one person in the car and they just feel entitled to use the fast lane regardless of how fast they want to drive. Like, they don't understand the concept of lanes being related to speed, and are just thinking, "hey I'm a carpool, I get to drive in the carpool lane!" or something.
I've seen people in 20-year-old Chrysler minivans packed full of kids go all the way over to the fast lane and proceed to drive 10 under the speed limit, followed by a parade of cars passing them on the right because WTF. I can only assume that they literally don't understand that if the other people in their lane are going faster than they are, they're supposed to move over to a slower lane. Or they just don't think about it at all. I have no idea.