this is the reason for protests.
Back in 1937, when the Madras Presidency government led by C. Rajagopalachari insisted on compulsory learning of Hindi in the State, the Dravidian movement, then in the form of the Justice Party, got a major campaign agenda. For three years till the policy was revoked in 1940, the agitations were sustained in almost every part of the Presidency, in the process making its leader, E.V. Ramasamy (Periyar), the tallest leader of the Dravidian movement.
In 1965, when the 15-year timeframe to make Hindi the only official language was about to expire, Tamil Nadu again led the agitations. By this time, with the Dravida Munnetra Kazhagam (DMK) gaining ground, imposition of Hindi was part of the narrative of the Aryan-Dravidian divide — the northern Aryans attempting to invade the cultural space of the southern Dravidians. It took an assurance from the then Prime Minister, Lal Bahadur Shastri, that English would continue as the second official language as long as non-Hindi-speaking people wanted it, to quell the protests.
Hindi is still a thorn in Tamil Nadu's flesh - The Hindu