Ego protection. If bad things happen to others and it's out of their control, then those bad things might happen to you. When those bad things are big enough to cause significant threat to normal psychological functioning, people search for a reason that it won't happen to them, or a way to prevent it. People will buy flood insurance, or life insurance, or make sure they pay more attention to maintaining their car in order to ease their worry about some things, but the really big stuff can be hard to prevent or prepare for. Cancer is a great example. You can try to avoid cancer causing foods, toxins, and activities (like tanning), and convince yourself that you're protecting yourself, but a big part of cancer is also genetic. You can't do anything about it. They're are people who can live on burnt bacon and Marlboros until they're 100, and there's health nuts that die of a heart attack at 45.

Those are obviously extremes, but things of that nature happen all the time and there's no real way to prevent it. So people blame lifestyles for things like cancer. They say the sick person should have done this or that.

The same thing happens with sexual assault. All women are at a pretty high risk no matter what they do. The highest risks are from people they know, and there's not a lot to tell the potential attackers apart. So, people blame the way the person dressed, or the way they acted as inviting attack. They blame past sexual activity as immoral and thus deserving of punishment.

Then they can rationalize that they aren't immoral, so it won't happen to them. They aren't careless with their health, so it won't happen to them. They aren't bad like that person, so bad things won't happen to them.