Even if some kid makes a video of themselves jerking off for their own personal enjoyment, unprompted by anyone else, if someone else gains access to that (eg a technician at a store or an unprincipled guardian) and makes a copy for themselves they're criminally exploiting the kid by doing so.
There was a cartoon picture I remember seeing around 15+ years ago of Bart Simpson performing a sex act. In some jurisdictions (such as Australia), this falls under the legal definition.
You don't think it's worse to molest a child than to not molest a child?
Huge difference here in Europe. CSAM is a much more serious crime. That's why e.g. Interpol runs a global database of CSAM but doesn't bother for mere child porn.