to give HOV vehicles a benefit of a faster commute when the other lanes are backed up. The problem is that idiots dart in and out of that lane when there is a single white line slowing down traffice since they don't know if someone will suddenly dart into the lane. It would be more effective if like in other states the lanes had a physical barrier between exits. (I personally have no qualm about speeders in that lane and often go 10 over in that lane myself.)
I do however have an expectation that people in the left "passing" lane will move over as soon as possible to let someone pass no matter how fast they are going as long as they don't have to slow down to to get into the next lane to let you pass.