--> The main reason lies in the fact that Indian women were not EXPECTED to earn and RUN the family. So, a majority of women restricted themselves to household work (Reasons may be anything from Strict family to disinterest). Out of the few who were working there was only a small percentage who had the HUNGER to grow in their respective field, which resulted in men occupying most of the high level positions.
But in recent times, things have started changing and families want their girl children to work and there is a lot more enthusiasm shown by women to grow in their jobs.