Why are girls so sexualized and slutty nowadays?

I dont understand why our society has degenerated so badly. Just on a trip to the mall, you see girls as young as 13 wearing very short skirts. Some of this stuff makes me want to throw up. I dont know if it's the media or peer pressure or whatever, but some of this stuff is just plain disgusting. Before the 60s, women(and men) were much more prude. Nowadays, everyone just simply acts on impulse. It's all so confusing. Why such a drastic change?