Why did Kumayl surrender?

Kumayl believed in Allah and the hereafter. He loved all people. He loved his family and his tribe.

Al-Hajjaj mistreated Kumayl's family and tribe. So, Kumayl surrendered to save them from persecution.

Kumayl remembered Imam Ali's words:

Kumayl, order your family to do good. Order them to help people at night.