This is not the only company servicing this route, this is a new company added to this route a few years ago, and the older company are still allowing electric cars according to the linked origin article at NRK. The route is also not a local one, running along most of the coast of the whole country, between the very north and pretty far south, so I don't really know if there is that much traffic only travelling a stop or two. Definitely a bunch of tourist traffic though.