Everyone who travels is not a super-knowledgeable frequent traveler who knows all of these brands backwards and forwards. Among the general public, Sheraton is a well known name, much better than Starwood, and adding Sheraton (or at least keeping Sheraton) to the 4 Pts name gets a lot of recognition from people who wouldn't recognize 4 pts, and these people would be much more likely to book a 4 pts than if there was no appendage or if the appendage was Starwood.