I know people who do the same thing with charitable donations. They donate to an organization because they "need the tax deduction". Despite that they'd have more money in their pocket if they just didn't make the donation in the first place.
I wonder if this is the result of most people taking the standard deduction instead of itemizing at tax time.
But that being said, a 15-30% discount because you used a different credit card to buy it is a pretty good incentive.
I'd venture that a lot of people are typing all this info into their tax software, which summarily throws it all away without them really understanding that that's what's happening.
Regular folks just do not get this stuff and it's silly that we have such a complicated system.