...is that the laws for their use is different from one state to the other. In the US, most driving laws are the same from state to state. Car pool lanes tend to be the exception in that some states have set entry and exit points, and others allow you to enter or exit wherever you want.

I've nearly been hit or hit someone in Utah due to cruising along and having someone jump into or out of the carpool lane in a place where they shouldn't be. So I wasn't looking for them to come into my lane - or, I was changing lanes into the passing lane and nearly hit by someone coming out of the carpool lane in a section of road where they should not have been.

Generally I agree with you - there are other elements to the carpool lane. And I admit to oversimplifying my view - mostly I was trying to express that the carpool lane is very different than the passing lane. At the same time - often there are people camping in the carpool lane who don't need to be camping there.