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.