Norway is able to put fewer people in prison because it puts more emphasis on crime prevention. The US chose a different a long time ago, probably even as far back as the war on drugs. It's going to be very hard to put the toothpaste back in the tube again, if that's even possible.
Besides being wealthy, isn't Norway pretty culturally/ethnically homogeneous? That may be a pretty important factor that may contribute to making their policy choices work.
Similarly, isn't it a welfare state? That could also play a pretty significant role, too.
I dunno. I'm an immigrant here, and my view might be skewed. That said, my own life has more diversity than it ever did in the US - I'm from the midwest. More types of folks. And I don't live in Oslo. That's no real reason that jails in the US can't be better and actually treat people like people that are going to live next door to you in the future. Being diverse isn't a reason to give long jail sentences or avoid jail/prison for more things. You certainly don't need a homogenous culture to do that sort of thing.
And yes, it is a welfare state, which means there are slightly fewer desperate people. I don't view that as a good thing - some of the folks here would just be left to die in the US. Some things also just mean a less stressful life - you know, like health care not making you go broke. It isn't perfect, mind you, and folks still fall through the cracks, but I'm sure it helps.
One could start by not putting as many folks in prisons and jails. You don't have to be a wealthy country to do that.