Because she is a very attractive woman with a rich family background who had a sex tape with a famous r&b singer. It leaked, and it went viral. She was also a stylist/organizer for Paris Hilton. Kris Kardashian approached Ryan Secrest and said "Hey, I've got a big crazy family that would make a good reality show." She had connections, Ryan pulled some strings, and wah-la! Kardashian empire is born.