Per capita income in India has been low due to:

Per capita income = National income ÷ Total population. The size of the population directly determines the average income per person. India's rapid and sustained population growth means national income has to be shared among an ever-increasing number of people, which keeps the average (per capita) income low even when total output rises. Hence population growth is the basic reason for India's low per capita income. Rise in prices, the rural concentration of population, and regional imbalance affect the value, location, or distribution of income but are not the fundamental cause of the low per-person figure.