Because ALL of the people in these videos are normally underage.
Who exactly do you propose we prosecute? And for what? This is a hard problem with no easy solutions. Principals all across the nation have been struggling with it, its just not as simple as people like to make it out to be.
Going after the person distributing the video seems obvious - distributing child porn taken without (one of) the subjects' consent is not a good thing.
You're misunderstanding how this normally develops.
I'll give you an example. Let's take the common version. Don't worry, I'll make it short:
Two 15 year old girls hang out one weekend and decide to take sexy pictures of each other. They share the photos with a few other trusted girl friends over time. Everything's ok, so far. Two months later, the girls are now "enemies". Or some girl in that small peer group, (clique), falls out with some other girl, you get the idea. One of them forwards pictures to a larger social group for the purpose of demeaning the girl or maybe demeaning multiple girls. BAM. Disaster. Photos are being forwarded everywhere. Parents are calling. Fights are breaking out in the halls, because maybe someone's brother is a hot-head. etc.
Now... who exactly do you prosecute for "distributing child pornography". The girl who was victimized by the bullying right? She was the one who INITIALLY forwarded the images. Do you see the problem school administrators face?
You are right; as the school administrator I am not going to wade into that he said/she said mess.
But I would call the DA and tell them there is a child porn "ring" in the school. Have them come in, subpoena phone records, and have a police detective read their rights and interview everyone involved. You probably only have to do that every 3 or 4 years to keep a lid on it.
So instead of one teenager who is embarrassed and emotionally disturbed, you'll have dozens who will go through life as registered sex offenders, constantly harassed by idiots who think they are child molesters, cut off from certain jobs, barred from living in certain neighborhoods, marked with the scarlet letter for something stupid they did when they were kids.
Did the police help solve our drug problems? No, in fact, they made society worse than it had been when drugs were legal; now we have teams of soldiers serving search and arrest warrants, all in the name of prosecuting drug offenses. Do you really want to bring that sort of chaos and mayhem into our nation's middle and high schools? Schools already have many of the characteristics of prisons; let's not make that any worse.
You can take a photo of anyone and distribute it as long as it's not libelous or commercial. Even if it's porn-y, if everyone involved is underage then it's going to be tricky to prosecute.
"I would prosecute the people who posses and distribute the child pornography"
In other words, you'll prosecute half the kids at the school. Just who do you think possesses these videos once they are released? Who do you think is distributing them?
Who exactly do you propose we prosecute? And for what? This is a hard problem with no easy solutions. Principals all across the nation have been struggling with it, its just not as simple as people like to make it out to be.