Because Modi is a Hindu nationalist and a majority of people from India are Hindu. His wide support has a lot more to do with the fact that he appeals to the majority with his supremacist rhetoric.
Calling Modi a hindu nationalist wipes out centuries of nuance from the Indian political conversation.
Hinduism has been the only religion over multiple millenia to shelter a plurality of other religions relatively peacefully despite being a demographic majority. India has accepted & protected related religions like Buddhists, Jains & Sikhs to Christians, Muslims, Jews, Zoroastrians and even Atheists. If anything, quite a few of these communities were able to become disproportionately wealthy and successful without any outright opposition from the Hindu majority. Practised Hinduism itself isn't well defined and would be construed as a different religion from house to house.
Just because an insecure protestant priest translated Hitler's hooked-cross mimicking his local austrian church as a swastika, doesn't mean that an entire civilization can be cast into the modern nazi/ethnic-supremacist framing of all communal relationships. Western commenters can't get their heads out of the western image of the world and consistently misread community relationships, beliefs and tensions in the non-Christian world. If the west had to cast India into their shallow oppressor vs oppressed narrative, history would reveal that the demographics that would occupy each bucket would be in direct contrast to their expectations.
Modi is no saint, but he is pretty conventional for an Indian politician. The Indian political divide has never followed western conventions. The questions of French secularism vs Nehruvian secularism has always been an open debate with good points on each side. The questions of whether India has a disproportionate responsibility to provide refuge to persecuted hindus in other nations is a valid question that other secular nations grappled with too. Similarly, ideas of formal voter ids and the ability of a majority government being able to pass bills with said majority are issues where Modi gets grilled for following the 'secular wests' footsteps.
There is a reason that despite western declarations of genocide every week, (traditionally western-liberal) Urban Indians keep voting for Modi YoY. A 100% of us might be hindu-nationalists cheering on a genocide, or western-media might be lying/misrepresenting the facts.
