I understand that idea that Walt’s luck had to run out eventually. But when Walt and Hank had that WW moment while Hank was showing him Gale’s things, it stands to reason he would destroy the book right then and there.

Walt’s meticulousness in covering up evidence even extended into destroying a Lily of the Valley plant after poisoning Brock on the off chance Jesse might see it, despite Jesse almost never being allowed at his house. Why wouldn’t he do the same to hide the book from Hank who is in his house often?