WTF? I guess, if you consider that most 13" don't use or would want a sometimes faster CPU a "marketing reason". They sell products people want. 13" buyers are clearly prioritizing size and minimalism above latest and fastest tech, which come with their own compromises. Cpu hasn't been the bottleneck in recent years, it is much more an I/O issue for rank and file computer users, not gamers but productivity users.Apple never offered a quad core 13" for marketing reasons because they want it thin ("design themselves into a thermal corner") and because, as the laptop line is now, it will cannibalize 15" sales due to lack of a decent performance gap.
A quad core 13" should be their dream come true
Not that you should be, but you might be out of touch what the Apple buying masses are looking for. Hint: it's not raw speed at any cost. Razer and many other PC manufacturers got that covered.