Why does homework exist if it causes so much long and short term stress, lack of sleep, and even depression in some cases? all of these things are extremely bad especially during the developmental periods that youths are going through. the list goes on along with the homework.

Your making this sound like homework was created for some evil purpose. If you feel like your being overwhelmed with homework you need to create a schedule for when certain tasks should be done. Making sacrifices where they are needed. If homework becomes so stressful and difficult to the point you become depressed you should consider one of the following

talking to a counselor and asking for easier classes.

focus less on sports and extracurricular activities

or be homeschooled where your homework is more pliable around yourself.