Why is the minimum available ISO sensitivity higher than usual when Picture Profile is set to S-Log?

The minimum ISO sensitivity is higher than usual because S-Log uses a different kind of exposure control to achieve a wide dynamic range.

S-Log2 and S-Log3 have gamma curves that enable recording with a wide dynamic range. When recording with S-Log2 or S-Log3, the camera controls the exposure differently than usual to achieve this wide dynamic range. This makes the camera’s minimum available ISO sensitivity higher. If the noise is significant when recording with a high ISO sensitivity, record with a brighter setting and perform grading after recording. Note that there is a corresponding decrease in dynamic range when you record with a brighter setting.

For details on S-Log, refer to the page below.
Help Guide for Creators
https://helpguide.sony.net/di/pp/v1/en/contents/TP0000909108.html

NOTE: Help Guide for Creators is a Help Guide for more creative image production using a camera manufactured by Sony.