Why Has Fashion for Teenagers been allowed to become so..."inappropriate" in some places?

I'm confident I didn't use the most accurate words in the title, so ill clarify a bit. In recent years, I have noticed a lot of teenagers (mostly under the age of 18) wearing clothes that barely cover their private areas, if not outright showing off stuff like their underwear. Specifically, I noticed it a ton among classmates in middle and high school (for some extra info, Im currently a teenager myself). Of course, I'll admit, my schooling is a lot more unique than most, so this might not be a widespread thing, but that still doesn't detract from the fact that its happened at least somewhere. For a specific example, in 10th grade, I saw a number of classmates wearing loose shirts with such large neck cuts that the cups (? I'm not 100% sure what theyre called) of their 30% see-through lace bras were always visible, especially if they leaned forward. There are guys who I've seen wearing super short shorts with obviously no underwear underneath. Once, I even saw a girl at my high school (I was in 11th grade, pretty sure she was too, or maybe 10th) wearing a small miniskirt with no underwear on at all. I was fucking shocked by what I saw, but didnt know who she was.

I get people wear and want to wear what's comfortable to them, but how in the world have (at least in my areas) parents and schools allowed these clothing choices for their children who are in no way adults? Yes, high school girls can very likely wear tanktops and so on just fine, but a 16-year-old going to school fully commando in a miniskirt is fucking insane to me. I cant be the crazy one here, can I?

Thanks for the answers.