What is the difference? It's easier to make money with the AI you get at each incremental step toward potentially destroying human civilization (though, of course, it's debatable whether these companies really are making money as such).

So what? You are implicitly arguing that human civilization will be unable to resist engaging in a large-scale, coordinated effort to destroy itself, just to make a few bucks along the way. Is this true? I don't know. The point of the nuclear analogy is that we have previously shown that we can, under certain conditions, put the eschaton back on the shelf for some period of time, despite very real pressure to take more incremental steps toward doom. "But AI can write code" is not a refutation of the possibility that we could take a more measured approach to AI development.