I found out about them because I wanted to see if I could find a wireless solution for use with an old iPod, otherwise I would have never been looking. People who already have wired headphones, and aux cords, don't need to find wireless solutions, because they already have an inexpensive solution that does the job. Even if you showed them a BT dongle they might pass it up as what they're using is good enough. Yet for many of those same people, if the headphone jack is removed and they are shown a wireless product, they might wonder how they ever lived without it.
That's how I felt when I started using my BT dongle in my car. It changed my whole communting experience.