Why my dataset generates wrong result？

My points and hull are as below:

<img width="641" height="645" alt="Image" src="https://github.com/user-attachments/assets/9a003dbe-4914-4e78-bb64-0ffd473ddb04" />
But the result is messy.

<img width="642" height="639" alt="Image" src="https://github.com/user-attachments/assets/e7a5ca4f-cbf7-44e0-973b-c057bad5805b" />
Why ?