2. Hank Has No Definite Proof Apart From Leaves of Grass Inscription, He Needs Some
Hank might have seemed like an idiot loud mouth in the first couple of seasons, but he has proved himself to be probably one of best D.E.A agents in the organisation. He's not going to ask Walt outright, he's going to build connections to the rest of the evidence he has, and eventually confront Walt with it when he has it all figured out.