Buttcoin

Because they're very stupid people.

That's a reductive statement, but it's basically the whole thing when you get right down to it. The entire rationalist movement - referring specifically to the Elizer Yudkowsky bastardization of the term here - is basically bad logic that appeals to people who think they're smart, but aren't actually smart enough to recognize it as bad logic. Elizer sells the fiction that smart people don't actually have to trust in experts or commonly established scientific methods because they can just deduce all the answers to the universe by applying logic. This presumes some kind of inherent superpower of intelligence and effectively teaches it's adherents to treat every presumption they make as scientific fact. This makes you very prone to reinforcing bad ideas, and makes you extremely vulnerable to scams that prey on your belief in your own intelligence. Crypto is the perfect version of such a scam.

There's also a massive overlap between rationalists and libertarians because a fundamental belief in the supremacy of your own mind, with its attendant presumption that the vast majority of people are incredibly stupid because they don't agree with you, tends to align very strongly with individualist philosophies. And of course, it takes a very special kind of stupid to believe that libertarianism - a school of thought that proposes that we privatize roads by building quadruple decker porous glass bridges, among other things - is actually a good idea.