Mumbai and Chennai are coastal cities with cable landings, but Mumbai is the finance and media capital - it has the stock exchange and Bollywood, both of whom I imagine will be big customers. And a bigger population as well.
Not exactly Bollywood, but VFX outsourcing is big in India. From low-cost animation (think animation for kids' TV) to top TV drama like Game of Thrones to Hollywood blockbusters like Interstellar and Doctor Strange -- they all use outsourcing and most of these companies are in Bombay.