Question

why did the Indian rulers opposed the british

Answer 1

This can be a long answer but I will try to give you a comprehensive answer. The Indian rulers did not initially oppose the British Trading posts in Calcutta. The British delegation sent to the Mughal rules was actually appreciated by them and the British were legally given the right to legal conduct all their trade, under the East India Company.
However, things got out of hand a little bit, as the East India Company became ever more powerful and even had it's own army. 
This was used for protection but the company started to become aggressive and actually took over large parts of the land. This is when the Indian rulers sensed a problem and understood that the British had, in the disguise of a company, other plans for India