I think it's not that complicated -- Kagi's search results are just far more useful. I think it's marketed at people who want good search results, not anything dealing with privacy (although, Kagi doesn't log your searches, so it's fully private for most everyday definitions) -- your viewpoint for you makes perfect sense to me and sure I respect it, but I don't think it's right to say that people are linking their credit cards to do a have-to-be-logged-in-first search on Kagi chiefly for reasons of privacy focus.

(I just tried the same experiment Doctorow tried, of searching for something that I'd been unable to find through Google, and Kagi did the same thing for me that it did for him (i.e. found it). That's actually not important enough for me to pay for Kagi, but "Google is shit now" is no fringe opinion and it's pretty easy to verify that Kagi does in practice work markedly better.)