What subject loves a biography of them unless it’s in the style of a hagiography? Few people like having the mirror held up. (Not to say that’s a wholly accurate heuristic)
My first thought upon learning about Schroeder was to recall that Lowenstein's book (which came first) was also poorly received by Buffett (but he grimly signed the book when presented with it).
Schroeder was the follow-up. She was given full access where Lowenstein was not.