Because Modi is from a lower caste. Upper caste Hindus cannot digest anyone other than themselves to rule. It is in their genes. The Brahminsm (Aryans migrate to India) started the caste system and idol worship destroying the Sanathan Dharma way of life prevailed in Bharatham, the land of the intellectuals.. (Bha means intellect. rath means to enjoy).
The Brahmins with the help of a section of the locals who were called upper castes harassed the lower caste majority by scaring them about God and exploited them never allowing them to live with human dignity. The lower castes converted to Buddhism, Jainism, Christianity, Islam and Sikhism to escape from the Brahmins and save their women.
The Mughals and the Europeans gave the Brahmins left right and centre. Still their arrogance remains even today, even though the fangs are now hidden. The Brahmins never learn. They still think they are the best people (?) in the world. No one really bothers them. They want the lower castes to carry them around to prop their self respect. People were afraid that the Brahmin priests could do something to make the God curse the people ! It is the same trick that all religious priests use world wide.. Scare people about God.
Even God is reportedly scared of these parasite priests. God absconds the scene like a Lion when the stinking hyenas approach.