They don’t cost double. In many cases petrol cars are still cheaper than their electric counterparts in Norway. Hyundai Kona petrol, for example, is slightly cheaper than Hyundai Kona electric.
But because of their tax exempt status, the price premium for electrics is much smaller in Norway than in most other countries.
I think it's much more newsworthy that 40% of cars sold use petrol, when they cost DOUBLE because of taxes.