Many of the high profile big budget attention grabbing games go for cinematic experiences with actors and plot stuff. When that's added to a racer it's often boring padding that distracts from the core racing gameplay.
I remember some awful racer on the 360 where your were bored out of mind ploughing though lengthy openings with tons of crappy dialogue and a stupid amount of time spent walking around on foot; the whole time just wishing you could get into a car and start the bloody game. I actually don't know if the racing side was any good because I didn't play much. Too much padding.
Also games tend to opt for rpg esk elements with elaborate upgrading mechanics. That's not in it self bad, it just seems to be everywhere and it's not needed everywhere. It means every single racer involves going though the same old menus with buying cars and tweaking stuff rather than just getting into the car and learning to drive fast.
I don't think Mario Kart would be as popular with that kind of padding between courses.









