Well, actually not so very many people wear fundoshi any longer.
They are primarily worn, if at all, on ceremonial occasions such as misogi purifications and other Shinto festivals.
I understand that they can be purchased now as a one piece unit that can be slipped on as if they were a pair of briefs. This is probably a good thing since many people no longer know how to wrap the fundoshi properly and they can come undone at the most inopportune moments. (blush)