Why was so much importance given to public sector in five year plans?

At the time of independence, Indian industrialists did not have the capital to undertake investment in industrial ventures required for the development of our economy. The market was also not big enough to encourage industrialists to undertake major projects even if they had the capital to do so. Due to the lack of adequate resources with the public sector to develop basic and heavy industries, the state had to play an intensive role in promoting the industrial sector. The decision to develop the Indian economy on socialist lines led to the policy of the state controlling the commanding heights of the economy.