Raspberry Pi Pico ADC changes the sampling rate in Free-running Sampling mode

I am configuring the ADC sampling rate here. Due to unknown reasons, the DIV register cannot be configured here. The actual sampling period is fixed at 65. Can anyone help me what is going wrong here？ <img width="551" alt="c39121a7385513c1579481977b0c62e" src="https://github.com/user-attachments/assets/5fb8eb58-d244-40c1-9607-16754808558c"> <img width="512" alt="b078a23843d708c1ae0b4c6966c8a88" src="https://github.com/user-attachments/assets/fe217690-835d-42d3-94e9-2bcbf0fc4925"> <img width="554" alt="a91a38f1944c012e122d14c44dcbc40" src="https://github.com/user-attachments/assets/9ffe2d0c-c3c5-4526-9309-010c16cedf99">