But WHY do people in real life do it, and where does that pressure come from? It is key to understand this.

Women dress that way in real life to attract men. In fact I would go so far as to say that the ONLY time it is appropriate to dress that way is to attract a man (or a woman if you swing that way). You might think that that's terrible, and that the only acceptable way to wear such clothing revealing clothing is for yourself, i.e. makes you more confident or something like that.

However, if that's true, and wearing sexy clothing makes you feel better about yourself, then you must not have a very confident self to begin with. So on one hand we aren't supposed to judge people on their appearance, but on the other hand your appearance affects how you feel about yourself?

Seems like a lot of women equate looking good for men only as an end to itself is a sign of weakness or submissiveness, enhancing their outward appearance while saying it's for internal reasons to justify it.

So the insidious part is that men want women to dress this way because it is appealing, but now women are deluding themselves into thinking they are choosing to do it in order to feel good. This is of course perpetuated by the generally male dominated media, which causes more women to 'choose' this behavior for themselves, and pressure other women into doing the same.