I think the standard explanation is that a huge country like the US lacks the social cohesion necessary to pay higher tax rates in exchange for social programs that benefit everyone. Like, I believe Sweden's population is about 10 million- much easier to have the social 'glue' for 'let's all agree to pay very high tax rates, and we'll all get collective social programs with it!' Versus the US at over 300 million people, you don't feel as connected to the other folks who would presumably be benefiting, and it's tougher to get a 'we're all in this together' mentality. Think of the difference in social cohesion between a small town and a huge city.
Like, I'm an American and I've literally never even been to most red states, never been to Texas, don't really know anyone from any of those areas of the country, etc. I don't feel a lot of connection with them.
Then there's, frankly, the racial angle. Most of the Nordic countries have traditionally been pretty ethnically homogeneous, which helps the social cohesion/let's all chip in for government programs together mentality. The US is of course not, and racial fears about 'those people' getting unearned benefits is a HUGE part of the American story.
Basically, the US is the most right-wing of the developed countries, and we tend to have bell-shaped unequal systems where a small % live very well and a larger % are below European standards. Healthcare is like the best example of this.
I've also heard a little talk that our political system is more amenable to lobbying by corporations than a parliamentary system, but I don't know enough about that argument to really advance it