Since the prior is uninformed, it's obvious this isn't "extraordinary claims require extraordinary evidence" since both claims are extraordinary. It’s just that one is political desirous. Ain’t fooling nobody with the attempt at rational cover.
Caplan shouldn't be surprised at the reception of his work, because people have this prior.
Of course as you say high priests of rationality examine their own biases as they reach for the book, and by the time they flip it to read the recommendations on the back they are already empty vessels for unadulterated pure non-chill-filtered high-octane data and nothing else. But most people working in public policy are just lowly humans. :/
Plus it seems despite his many spreadsheets his model is not able to do causal inference, which means his tables are very verbose narrations or appendices to his arguments in prose, and not a decisive proof.
> to change your mind
Unless one is in a state of 100% confirmation bias then ideally every little piece of evidence counts. Sure, we are not perfect walking-talking sentient infinite resolution mathematical distributions, so in practice we simply discard a lot incoming information, as we have meta-(meta?)-heuristics that we depend on. (Eg. if our friends and family and the news and even random blogs claim X we start to take it seriously, but still, if it doesn't really affect us our attention won't bother. And so on.)