Because love for Ali is faith, and hate for him is disbelief. But rather, the Paradise was created for the people of faith, and the Fire was created for the people of disbelief. Therefore, he is the distributor of the Paradise and the Fire due to this reason. So the Paradise, none shall enter it except the people who love him, and the Fire, none shall enter except for the people who hate him.
Imam Ja’far al-Sadiq (ع) Illal al-Sharaie v. 1, ch. 130
Al Mufazzal bin Umar (ر) asked Imam Ja’far al-Sadiq (ع), ‘Why did Amirul Mo’minin Ali ibn Abu Talib come to be Distributor of Paradise and the Fire?’ Imam al-Sadiq (ع) replied…