Ice is very different to snow to cycle on.
During winter the sidewalks rarely get the snow removed. So unless there's dedicated bike lanes, which there are still rather few of, you'd have to bike in the middle of the road. Which, due to the topography, would mostly mean holding up the traffic big time.
Here are some news articles from last winter which contains some illustrative pictures: https://www.aftenposten.no/norge/i/m60VB0/Mer-sno-i-vente-pa... https://www.aftenposten.no/osloby/i/ka3kLj/Oslo-vinteren-har...
Of course it's not always that bad, but it's usually not a whole lot better either for most of the winter.
They've also said they'll focus keeping the bike roads clear during winter, currently a big issue for myself.