I agree with this. Their goal is to get people to buy the stuff they normally wouldn't. They know you're already going to buy your normal items, so cutting you a break on those doesn't help them. Instead, they want you to buy that steam vacuum that you'll use a couple times and then forget about it or realize those messy kids never give the time to use it.
(Used to work at Amazon, but back then they didn't have Prime Day yet).