Nuclear weapons still aren't easy to make by any means. It's not so much the nuclear physics that's the challenge as it is all of the engineering best-practices. That, and the difficulty of obtaining raw materials.

And nuclear weapons aren't a binary either. North Korea has demonstrated the actual bomb, but their delivery systems are still far from reliable. Their rockets might technically have the range to threaten the US, but what are the chances they could actually hit their target? And how many launch vehicles do they realistically have? Not likely enough to seriously threated any other nuclear powers. And this after making decades of enormous political and economic sacrifices to pursue nuclear weapons. I don't think most countries will feel tempted to follow their lead.

You don't need 100% reliance on ICBMs if your only aim just to hit enemy's mainland for the sake of it. Cheaper means are on the table.

Much more relevant theatre range weapons are things even NK can manufacture. I was very surprised to learn that North Korea not only designed a working cruise missile with their economy, but had a working terrain hugging flight on it.

This got me thinking about the common misperception of how empty the Earth is:

If you dropped a bomb of a certain type and strength on a random coordinate in <country> how many people do you kill on average?

On average, or by percentile? Because I think one is more likely to be revealing than the other.

A 1Mt device might only have a 50% chance of killing 1+ people if detonated at the proper altitude at a random location within the US, (47% of the US is uninhabited) but average 1000 deaths (~6mi lethal radius, US overall population density of 90p/sqmi).

Good point on that. Yes, you've described my thought in much better detail.