Because let's be honest, most private pilots will hardly have a clue what a mode-S transponder really is, compared to a mode-C transponder.
Correct, Exhibit A right here,,, ME
Got a question about mine, its one of them fancy new ones that you don't have to turn on prior to take off, when I do a N reg check on the FAA website it lists my plane as having a "Mode S code" which is 8 digits, what does this code mean? it is a unique code and not the aircraft serial number.