Although the Kardashians had divorced and Kris had remarried Bruce Jenner years before the murders, she had also been close friends with the Simpsons, particularly Nicole, and was drawn into the spotlight to some degree in the media coverage.
It's true that Kim's sex tape scandal predated the reality TV show by several months (I had to look this up on Wikipedia, by the way), but she was actually known to some extent before the tape was even released-- partially due to her family's connection to O.J., partially due to being part of Paris Hilton's crowd.
It's so strange-- Tyra lectures the models about not looking too "hoochie" or "men's magazine"-- even eliminating a couple for being too sexy-- and makes a BIG deal out of her own limits in her modeling years, "being positive role models for young girls," blah, blah, blah.
And then she turns around and has Kim Kardashian as a guest judge on the show. Eeeeeeyeah, Tyra. Way to inspire them.