See through dresses...what is up with that?

So I work in a restaurant at a University. The restaurant is in a large building that is basically a big food court. I see literally 5000-7000 students every day...going by the typical ratio of the United States and particularly that age group, way more than half of these students is female...now taking into account that I don't actually notice every single female that walks by, I am going to guess anywhere from 50-100 college age women come by my restaurant every day in dresses that can be seen through fairly easily...also, this is indoors with a mix of indirect sun and artificial light, so these dresses would be transparent in bright sunlight...my question is, do girls wear things like this on purpose? or are they actually unaware? I just think it unlikely that they would look in the mirror and probably ask their friends how they look and no one would notice the see-through quality of the dress...