Of course it's who they approve of - because the point of carpool lanes is to effectively remove significant traffic and air pollution, and they felt that Uber doesn't qualify.
Bullshit, they're still letting licensed commercial vehicles use the HOV lane. The fact is that HOV lanes are shit. They're a waste of space which accomplishes none of the stated goals. Simply adding another general lane does more to reduce emissions, because it does more to reduce congestion, and thus reduces idling — where vehicles without start-stop systems get 0 MPG and thus are producing pure pollution. They're always trying to justify the existence of HOV lanes with bullshit like this, but they still are unjustifiable.