If you wanted to know without reading (or re-reading the whole thing), I added two items to the end: One is for the allowance of single races against the other seven characters without having to play an entire cup. I can’t remember which games do or don’t have it, but Mario Kart 7 doesn’t, so there we go.
The other, much more important thing (in my opinion) is individual endings and character victory themes. Super Mario Kart had them, simple as they were, so why not newer installments? They make a great motivation to go back and use each character to win a cup.
Check out both items explained in more detail (and with some video!) here.