I have a related theory (well, more like a wild-a** guess): while the solo loop band was judged the "most comfortable", it wasn't the most comfortable for everyone which is why the dual-band exists. Furthermore, I would guess an older prototype had a band from the headset going over the head to the back. Think of a solo band with a fabric strap going from the back to the headset. This was possibly even more comfortable than the current solo band, but it was judged to be too fugly/un-Apple-like, and so it was dropped.