Because even fraternities' lawyers are not idiots, and they know that nothing good would come of that, even if it could be proven that Jackie's telling the story to a reporter was tortious (which it might not even be).

The full report mentions that her lawyer told her not to talk to them, when they asked her for comment. So she has a lawyer, possibly because she is being sued, or anticipating being sued.

Any lawsuit would not be filed until today anyhow - this report is a major piece of information.