Given that politics in most countries is corrupt (or outright authoritarian/dictatorship/totalitarian), why are you astonished that the US is any different?

I see this sentiment a lot -- that for some reason the U.S. naturally "should" be a well-run developed country, and so it's surprising that it scores worse on various metrics than, say, Western Europe. But why? Is it just because the US is wealthy? Saudi Arabia is wealthy too and an absolute monarchy.

If it's not fair to compare the US to Eritrea, then it's not fair to compare it to Norway. It just is what it is, somewhere in between those two on the spectrum.