Darth Vader is a sadist who enjoys letting his prey dangle and twist for a while before they realize they’re on the hook. It's a coping mechanism.
Since he extinguished the Jedi, Darth Vader hasn’t seen a decent foe in years. You think your 9-to-5 is boring, but you get to go home at the end of the day and watch Netflix. Vader lives his dead-end job. There’s no advancement in sight. No friends. No challenging work. He probably doesn’t get invited to the company potluck, either.