Because it's a little bit similar to exploiting the snot out of a loss-leader product- a good-faith offer extended to generate some good-faith business, that is

Because it's a little bit similar to exploiting the snot out of a loss-leader product- a good-faith offer extended to generate some good-faith business, that is frequently a good thing for everyone. You are exploiting a complex promotion system by finding tiny loopholes, at the expense of everyone else (because at the end of the day, the banks will get their money...) And no, you can't argue that "because the loopholes exist, that's proof they don't care". Or another comparison, a white collar criminal who embezzles his company but found a legal loophole that means he can't be charged. Just because it's not illegal, doesn't mean it isn't immoral!