It makes sense if you view the HOV lane primarily as a way to reduce emissions, not traffic. This is also why e.g. single-rider motorcycles are often allowed to use HOV lanes as well.

buying an EV does not actually reduce emissions like magic, unless the owner drives that car for a looooong time. Like 10-15+ years.

Manufacturing an EV car uses a lot more emissions than an ICE car initially, due to the huge battery.

If the goal is to reduce emissions overall, then target incentives appropriately:

- tax deduction at purchase

- tax deduction for drivers of old (10 yr+) EV vehicles.

This incentivizes EV purchase AND driving that vehicle for a long time. In contrast, allowing EV drivers to use a carpool lane does no such thing IMO.