Diwali in North India is different from South India, So much so, that the same festival has different names. The stories behind the Deepavali in the south and Diwali in the north are different.
They call it Deepavali or Narak Chaturdas
Tamils, Telugus and Kannadigas celebrate Deepavali (not Diwali).
Kerala in the south does not celebrate Deepavali. According to a belief, in Kerala, King Bali’s death is associated with this day. In the south, it is not about Rama returning to Ayodhya, but it is about an Asura (demon) called Narakasura being killed by Krishna or Kali (Sakthi).
Another reason they celebrate Diwali since it is believed that this is the day the Jain Mahavir attained Nirvana (it was supposed to be on 15 October 527 BCE).
Some 30 years ago or so only a small fraction of Tamils, say like 10-15% of the people, celebrated, even in a big city like Chennai (then called Madras). The number of people who are celebrating it has now increased, but even today, in spite of its popularity, it is not the majority of the people, who celebrate it.
They don’t really connect or identify with the festival.
On the other hand, it is the biggest festival of the year in North India.
There a buzz, a vibe of Diwali in this part of the country. It is celebrated for five long days, starting with Dhanteras, Choti Diwali, Diwali, Govardhan Puja and concluded with Bhai Dooj. North Indians celebrate Diwali because of the popular belief, which is, Lord Ram with his brother Lakshman and Wife Sita returned Ayodhya after 14 years of exile.
It’s pleasantly surprising how people of the same country celebrate one festival in different ways because of different beliefs.
This truly reflects the diversity of the nation in an exquisite manner.