+3! Also more ‘modern.’ (And more $ for Gillette.) Great marketing won the day!!
Yeah, but marketing can only go so far to turn a sow's ear into a silk purse, or else we'd have all been using Techmatics. The Trac II had the advantage of actually being easier to use while giving shaves of generally acceptable quality. It just doesn't matter that a DE wielded by careful hands can give a shave of better quality than a cartridge when 90% of guys don't need that better quality shave or care about putting in the effort to get it.
And let's not forget how big the disposables got to be in the '70s too. Gillette was having a bad time by the mid '80s because their disposables were doing so much better than their system razors. Disposables meant your whole razor was always clean and fresh too, you didn't have a grimy lather- and dust-covered handle in the drawer.