A lot of "loud" generalisations here or whatever here, ignoring the finer bits. I am a bit drunk, but I will tell the story as I've been told.
After WWII, the labour party in Norway took dominance. Their origin were communist-ish, and their sentiment, in broad strokes, were like that: the people should "seize" control, seize the means of production, and use it to create a society which used is resources to benefit the people. Later, the party turned its back on these roots, and turned to a more moderate way: Bernstein, a german thinker, argued that capitalism didn't "collapse", or eat it self up or something like that, as Marx predicted (?), but rather just worked, in a way. So Bernstein, and others, proposed that rather than overthrow the order, (by force) they should try to moderate, and control it, be reform. From that-ish, social democracy was born. The workers should seize power and control the market and society, to better society for all. I mean, why not (it seems self-evident)?
So, the labour party nationalized the oil (when they discovered it, US companies was at the door, and all natural resources, saying it belonged to the people, and thus could never be sold. They wrote it into the constitution. Again, why not? The workers took political power, and used it to control the "flow" and development of society. They set the term, squeezed the capital owners, but just so much that it would still be attractive to do business. And, in addition, we had oil, and fish... well, everyone wanted it - so why give it away? Why not control it to our benefit? If we have "gold", why give it away?
Plus, from our roots, the population was not divided, of one culture, and the communist emerged from the war as saviours and heroes. Even today most people have backgrounds, and remember, their small towns, and their background of families with simple means: People were frugal, from farming background, homespun and all that, so perhaps thay was why no mafia or anything emerged here, when unions and such developed. Everone knows everbody, it's that kind of vibe, a bit exaggerated. Even today the trust in society, and to the state etc., is sky high. I don't even bother to check my tax returns, I trust the civil servants to do it probably. If I pay too much, I even get interest on the stuff I'm owed.
Fast forwaed, the same-ish principle stands. The labour party rules to share and create wealth for everone, equally. Even if they don't have power: Even the "right wing" parties here are for the same thing (if someone proposed otherwise, e.g. "leave the poor to die", they would be seen be all as pariah, like animals, and shunned by all. It's unheard of, such atrocious attitude would make you appear worse then the worst. the right wingers just want to make it happen through private sector, while the leftists are for doing it through public sector, broadly speakers. Could have said more, for example about the three part collaboration etc., but let's leave it at that. Take it all with a few pints worth of salt, it's enough for a start.
But, I would emphasize, us having such a homogenous population, a kind of stable culture were everone shared the same principles, background etc. - I think that played a big part. Even today, most people believe the integrity of politicans etc. to a high degree. Even if we bicker, it's more like family arguing. Heck, even the children of the crown prince attended public school; the king himself rode the tram when oil was in shortage (a very iconic moment in norwegian history - even if he probably rode with his chaffeur 98% of the time, the principle still stands).
inb4 oil bla bla bla, Sweden has the same welfare level (even though, here my knowledge is more very luck limited).
Thanks for reading, it rocks here (economically speaking; socially, it's as dry as bones, we are probably worse than the finns). Love you all, Cheers!