Hey, haven't you heard of Rocky Mountain Oysters?
While the idea of it may bother us, dried bull penis is perfectly healthy and safe. My guess is that it got popular because it is cheap. The guy who runs a pet boutique near me says he used to carry pigs feet, but they've gotten really popular as a gourmet item, and are no longer an inexpensive dog treat.
I believe that Flossies are just a cow tendon, not any ah, organ meat. There are lot of other things available: hooves, pig tails, and pig ears, to name a few. Really, it's just a piece of cow. It's not like the bull is using it anymore.