Most people never had a deep theological understanding of religion.
Mass Literacy only became a thing in the 20th century.
There's a reason why folk religions and customs exist (eg. Folk saints in Mexico and Southern Europe, the entire Chinese Folk Religion, Pir Darghas and Dervishes in Islam, etc)
Also "Hinduism" is a broad term for general folk religious practices in the South Asian subcontinent. For example, in the Himalayan region I am from you will see people revere an Iranian origin Muslim preacher who came to the area in the 13th century (Lakhdatta) despite also being "Hindu" or "Sikh"