The main reason for the growth and importance of mumbai is tje huge and popular bollywood industry which makes excellent bollywood or hindi movies.
mumbai was an important trading center the portugals named it bombay bom=good bay=port all the trading ships came here and made rapid growth of the city . Industries developed here and the growth boosted after founding bombay high a petrol providing center. it is not developed by the actors living there lol XD
Because birth rate is more and it is importent because it is known as film city and so many actors and actress lives there