I think it's because the Johns are looking for a chick that is at the upper range of possible - a lot of ugly men would be very thankful to have that chick.
The crazy thing is that the men aren't actually paying her for sex with them. They are paying for seeing her naked body through an electronic screen, which is less expensive than getting her to have sex with them. It's pathetic because they aren't getting sex out of it.
Kimmie is the poster child for chicks that develop early and look banging at age 12 (i.e., that was her age when she was discovered by the paparazzi at the OJ trial (her father was OJ's friend and personal lawyer - not the co-lead defense lawyers. who were Shapiro and Cochran) tend to just get fat as an adult.
There's some revisionist or inaccurate history here.
Kim Kardashian was born in October 1980. She was 13 at the time of the murders and 14 when the trial began in January 1995.
Also, once the trial ended in October 1995, right before Kim's 15th birthday, she wasn't a big deal at all until the early 2000s, when she made that sex video was Ray J and appearances on The Simple Life with Paris Hilton.