I agree with Tinks. It really is just as simple as that: people don't listen. I don't think it is deliberate, usually. They may try, they may think they succeed, but really, the average person just has really poor listening skills. To those of us who do pay close attention, at least some of the time, this can be very frustrating, but it is important to think of it as something over which people have little control most of the time - at the very least, far less than they think they do, anyway. I think that makes it easier to forgive and forget.