We don't really know why GT6 didn't include the GT5 version of the course maker, shuffle races, top speed runs, various photomode areas, or endurance races. They were all in GT5 which was on the same system, so it's hard to see why they wouldn't include them. But they didn't.
You can assume that they'll do the sensible thing, but you can't really state it as an obvious fact when there's ample evidence of them doing the opposite very recently.
GT trailers have dubbed sounds for a long time now. Everyone always wets themselves at how awesome they sound, only to get in game and find that it's nothing like it.