There is no mandatory voting in India. So, this question is incorrectly framed. I think what you meant to say was, "Should voting be made mandatory in India? Why or why not?"
No, it should not be mandatory. India is such a big country. It is really hard to enforce such a rule. Even if it is enforced, uninformed people will be taken advantage of by the police, etc. Moreover, seeing the condition of most of the politicians, I do not feel like voting. Why should I support the best amongst the thieve? I don't support any thief (Most of the politicians have charges pending which are much worse than thievery.)