My 13 year old girl lives with us half the time. Her other parent the other part of the time.
They let her keep her phone with her all the time. She can completely skip sleeping entirely for more than 2 days when she has her phone all night, texting with friends. She's having fun, but then she crashes and burns HARD when she comes back to our house. Get's sick, can't focus, emotions out of control.
At my house we take her phone away at 10:00pm, and she is passed out 5 minutes later. Funny thing is, I sometimes take away the phone on Sunday, in the afternoon, and she will pass out 5-10 minutes after that too.
Her body just needs a lot more sleep than it is getting. This is probably true with a lot of adults too. We use electronic stimulus to keep us going far beyond our "natural rhythms". Take those away and people can sleep.
If the natural rhythm of a teenager is to be unable to sleep until 2:00am, what are they supposed to do if they ever change time zones? People may have a naturally tendency to be a night owl or whatever, but that is hardly the most important element in the sleep deprivation story going on right now.