What keeps India together?

In Europe, I have met so many people who are really interested in Indian culture. They repeatedly ask me how is it done in Indian culture. I find it so hard to explain that there is nothing like a single Indian culture. For all practical purposes, each of the 28 states/regions of the country have totally different language, culture, tradition, history. Even inside a state, the rural India and the cities are totally different.
Two words have always amazed me:
“Dada”: In North India it means Grandfather, In the Eastern India it means elder brother and used to address a person with a lot of respect and social standing. However in the Southern India Dada is used to brand a notorious muscle man or someone who lives in the wrong side of the law and terrorizes the people.
Second word is the name of a loaf of Baked Bread. It’s called Double roti in the Northern Western Part of the country which means it is twice the size of the Roti (or the standard wheat dish) While in the south Western part of the country it is called ‘Pav’ or ¼ the size of the standard Roti. Incidentally the Roti in both the regions as well as bread are of almost the same size and shape.
Coming back to the discussion: It makes me ask the question what keeps the country together? Is it that Indians are too lazy that they don’t care about their governments and policies and want a status quo? I would not like to agree to that hence I tried to find some universally practices cultures and passion. The only 2 things I could find were our love for cricket and bollywood movies. But then is our rich culture so shallow that these two frivolous passions can keep us united?