Just because she is busty no!
Kim Kardashian is famous because of her history as Kardashian first gained media attention as a friend and stylist of Paris Hilton the most famous celebrity, but received wider notice and fan following after a 2003 sex tape leaked with her former boyfriend Ray J (a famous singer) back in 2007 and because of that PornHub still ranks her in top pornstars list. Later that year, she and her family began to appear in the E! reality television series named "Keeping Up with the Kardashians" and that was a hit.
After all of that, she begin her career to be the viral celebrity by breaking internet with her fully naked photos and also she have some apps and one app of her is paid where she uploads her private photos or maybe videos which can be seen by only paid members of the game app (app is basically a virtual world game where everybody can live with Kim).
Now everybody wants to see her and her body parts, that's why she is famous. The #1 reason for her fame is the sex tape. Just look at her:
Thanks for asking.