Earlier quoted context omitted.
Certainly the assumption that every intelligent agent will want to recursively self-improve is unwarranted. But it only takes one intelligent agent that wants to self-improve for the scary thing to happen.
Why wouldn't it if it is able to? It doesn't have to "want" to self-improve, it only has to want anything that it could do better if it was smarter. All it needs is the ability, the lack of an overwhelming reason not to, and a basic architecture of optimizing towards a goal. If you knew an asteroid would hit the earth 1 year from now, and you had the ability to push a button and become 100,000x smarter, I would hope…
Sometimes "accumulating more resources" is the most effective way. Sometimes "better understanding what problem I'm trying to solve" is the most effective way". Sometimes "resisting attempts to subvert my mind" is the most effective way. And yes, sometimes "becoming better at general problem solving" (self improvement of one's intelligence) is the most effective way.
But there's no guarantee that any one of those will be a relevant bottleneck in any particular domain, so there's no guarantee an agent will pursue all of those drives.