Why do parents never want to let their teenagers have their own privacy?

Not all parents are the same. My son had his privacy from an early age. Unless I felt there was a reason he needed watching , I respected hi privacy. He turns 21 in a couple of days and has never given me any reason not to trust him.

My kids all have & had privacy untill they gave me a reason to take it away.

Because every parent was a teenager once. We know what you want to do with it. ;^)

Well now that is not true with all parents. We have a 14 year old boy and we respect his privacy just as he respects ours. All teenagers deserve to have some privacy especially when they are doing nothing wrong to anyone else. Perhaps talking with your parents about this issue might help. "At least try it it can't hurt and you might be surprised at the ending.

they're either overprotective or just afraid that their child would land in some big trouble or make a huge mistake in life

some parents care about their kids so much that they want to make sure they're not do anything bad so they "invade" their privacy. its a show of protection

Some are control freaks.

However most are sane humans who know just exactly what your getting up to and don't want to find out later that their sons on meth when they could have stopped it.

Cause they know what we'll do with it xD

Maybe when they were teenagers they did things that they don't want you to do as a teenager now. Or (and no offense because I don't know anything about you) maybe they're basing their disciplinary judgment on what you've done in the past.

Not all parents....my family gave me my privacy but i am sure they were watching what i was doing. Don't forget before you became a teenager you were involved with them...they got used to that. It's so hard to let go now. Just give them time.