I think a lot of the girls who wear the hijab that way are the ones who are pushed into wearing it by family or others so they basically do the scarf bit and then just push the boundaries that have been set for them as much as they can, kinda like those girls in Iran who wear their hijabs right back on their heads and show as much hair as they can get away with.
I really don't want to judge anyone, but I dunno how true this is. Back in college, there were several hijabi chics, who whore the scarf on their head but super tight jeans, super tight short shirts...etc....any tight pants...that left nothing to imagination....but I am not sure if they were forced. These same girls would have the nerve to go around lecturing others on how Allah will punish them for not wearing hijab..etc....and just looking down on others because they thought they were high n holy....I used to get a kick out of that crowd. I give credit to those who wear hijab with good niyyah and are trying, and don't judge others, regardless of how they are, cuz at least they are trying. But I really hate the fake hypocritical ones.
I remember wayyy back in high school, there were these 2 egyptian twins who called themselves with very american nicks, like Nancy/Jenny. I had no clue they were muslim, cuz in the beginning they wore tanks n shorts to school, mini skirts etc. In the 1st year got to know em a little as they were in my Homeroom. Anyways one monday morning, they came to school suddenly covered head to toe & wearing scarves, everyone was like huh? (i had no interaction with muslims/desis besides immediate family at all). And they said they are muslim etc.....im like oh friday u werent muslim huh? lol
But since then they were ALWAYS trying to preach to me, and even went so far as to writing me detailed letters of how I am going to hell because I don't cover my head. I thought they were psycho. Mind you i normally wear full sleeves, back then very baggy clothes etc. When I didn't "adhere" to their letters, they stopped talking to me and ignored me, which I thought was great cuz they were freaks. Now my luck, they went to same Uni as I did....and what's funny is they saw me at orientation and acted so buddy buddy like we were best of friends. I HATE fakes with a passion.