Why do Keralites worship only Vishnu and not Shiva?
A small correction to Chidanan’s answer. Aadi Shankara preached and familiarised Adwita philosophy and not Dwaita. Adwita is no two implying only One. Dwaita means there are two. Yes. Kerala has many Shiva temples. People worship there with out any discrimination.Generally Hindus do not have any strict rules as to worship only one God. Even Aadi Shankara who is supposed to be a Shiva worshipper, has written hymns on Vishnu–‘bhaja govindam. Generally in Hindu mind there is no distinction about deities. “Hariyum Sivanum onnu; Ithai ariyathavan voil mannu”-This is a village proverb. Meaning: Vishnu and Shiva are One. To one who does not know this will get only sand to eat.