Great question.
This Mother Jones article explores the topic more fully. Here is a snippet:
The International Olympic Committee (IOC) says the women’s exclusion isn’t discrimination. President Jacques Rogge has insisted that the decision “was made strictly on a technical basis, and absolutely not on gender grounds.” But female would-be Olympic competitors say they don’t understand what that “technical basis” is. Their abilities? They point to American Lindsey Van, who holds the world record for the single longest jump by anyone, male or female. (Ironically, she broke the record flying from a jump built at Whistler for the Vancouver Olympics). Their numbers? When the IOC voted in 2006 not to add women’s ski jumping, 83 competitors from 14 nations jumped at the top level, less universality than required to add a new event. But in the same year, women’s skier cross claimed just 30 skiers from 11 nations. The committee added it. (There are also too few male ski jumpers to qualify, but as one of the original 16 Winter Olympic events, their event isn’t subjected to the same rules.)
Here is an article on the subject from Time.
Having gone to high school with Van and a few other female jumpers it does seem a shame that each winter Olympics that rolls around their petition to be included is denied. An epic fail on the IOC's part if you ask me. But that's just my two cents.
I agree, Susanna. Thanks for the comment.