There are only 24 hours in a day. Being a teenager, I should be getting 10 hours sleep. That leaves 14 hours to do stuff in.
For good health I should be exercising at least half an hour. That leaves 13.5 hours.
I have, say, 4 hours of homework to do a day. That leaves 9.5 hours.
Now, on an average weekday, I spend about 7 hours at school. That would leave me with only 2.5 hours left. Guess how long it takes me to get to school and back? 2.5 hours.
So if I did nothing but work and what is considered necessary for good health on the average school day I would not have enough time to even have breakfast or dinner. Unless I started multi-tasking.
Is it any wonder teenagers are sleep deprived?