There is a pretty simple yet disappointing reason. CSAM is much easier to investigate and prosecute. You got evidence, you prosecute. Almost guaranteed conviction. You can even enforce big tech to implement proactive monitoring systems.

Compared to this, CSA is much harder. Every case is different. You have to do due diligence. And it is extremely hard to proactively detect them. Careful criminals will destroy all evidence. The number of case itself is smaller. And there is a good chance to lose in the court and for prosecutors this is a clearly risky move. Good ol' criminal investigation is expensive. There is a structural reason not to prioritize them.

The whole incentive structure is broken. The only thing to fix this is external pressure, but even it does not work these days. Exposing CSA is a rare event but media needs constant, sensitive headlines so they tend to treat CSA and CSAM like the same thing. Hence external pressures do not work, and even worse those work in a wrong way. This creates a bad feedback loop.