Whitney died three years ago, yet her catalogue isn't nearly as recurrent as Bob's despite her having a much bigger career. So there goes your logic, yet again, 'he's only doing well because he's dead!!! ;;;p'.
Literally THE only other act who died decades ago with a Diamond album in the Soundscan era (1991-present) is The Beatles with '1'.
That says a lot if the only other retired artist rivaling his catalogue activity is The Beatles. Give the props and keep it moving.