I feel I should reiterate that I agree with you. I'm not seeing an in-universe reason for Voldemort's behavior in these two chapters either, except for maybe "He was overconfident and didn't see the need to take such excessive precautions", which isn't all that narratively satisfying, though it is somewhat realistic. (The planning fallacy is a thing, after all, and even Tom Riddle Jr. Sr. isn't immune.)