Simple. They're raised that way by their parents.
Consider this, via CatholicVote.
Retailers make clothes for girls in single-digit ages that are designed to increase the girl's sex appeal and invite boys to treat them like objects that exist solely to give them sexual pleasure instead of treating them like, you know, actual human beings. Then the girl wonders why she can't find a good man that actually loves her-not a man that "loves" her body, but rather a man that loves her. She is, from six and seven years old, taught to flaunt her body in a sexually appealing way. The clothes marketed to girls that age (ok, girls of every age, but bear with me) are designed to make her body more sexually appealing.
Now of course, that's not according to God's standard of treating the human body, especially the female version, as His work of art, His greatest masterpiece of physical creation. Rather this sex appeal is according to the world's standard of treating the human body as an object of lust, such that it is not good for anything but being taken advantage of for lustful pleasure.
Now these girls are not old enough to drive (some are a full decade away!) and aren't old enough to have a job. Where do they get their clothes? Parents. Who drives them to the mall and pays for their clothes? Parents. Not any of their friends or anyone at school, but the parents. Parents are the ones getting their girls these clothes. Parents are dressing their girls in a manner that puts their bodies on display as objects of pleasure, contrary to their actual beauty as God's works of art. Some parents want their girls to look like tramps, others find it harmless fun. Then the girl grows up and can't find a man that respects her instead of just her body no matter how hard she tries. No surprise. Cause and effect. Why is she treated like a tramp by men? She was raised to dress like one, act like one, and invite boys to treat her that way.
That is how society treats women. Society can't properly respect women because society doesn't respect God. You'll never respect the art if you don't respect the Artist. Society can't survive without God. Without God, we do nothing but manipulate each other and take advantage of each other. We need no more proof, this has been going on for thousands of years. The only reason to rebel against the strictness of traditionalist, orthodox, Catholic morality is out of a desire for pleasure, no matter how many people you have to disrespect to attain that end.