Diwali literally "Festival of Lights" is the most important festival in Hinduism celebrated all over the India with a very with a great joy. However there is one place where people don't celebrate Diwali at that extent as celebrated in other parts.
Kerala is the only state in India where Diwali is not a major festival. The native people of Kerala do not celebrate Diwali. People in Kerala are bounded to their culture and ethnicity and they have managed to preserve their customs and traditions that come with them.
In Kerala Onam, Vishu and Shiva Rathri are their major festivals. Onam is one the oldest festival in India and the cultural heritage of Kerala comes into full bloom at this time.People in Kerala don't celebrate Diwali, Holi, Rakshabandhan, Dussehra as like celebrated in North India.
Kerala was somewhat geographically isolated from the rest of India until the British colonized part of it. So there have not been any large-scale cultural exchanges with the rest of India. In fact Kerala had more cultural exchanges with Central Asia.