California isn't flat, either. That's one of the issues. It is a little different proposition going over the mountains with electric, than diesel. If they really did try to get rid of all diesel OTR trucks, it will spawn a huge amount of truck stops at the state border, greatly increase train freight traffic (thus slowing down delivery), and possibly impact port traffic from overseas.
The railroads could electrify a LOT easier than the trucking industry, at least so they could get freight over the border into neighboring states.
Oh and don't forget the additional wear and tear on the roads. More trucks, and heavier, to move the same amount of weight.