4) Presence of city loyalties
Football leagues are based on the concept of intercity rivalries. This is apparent anywhere in the world. The most famous of them all is probably the Liverpool-Manchester United rivalry.
In spite of the IPL, cricket is yet to catch up on this. People tend to support their favourite players and their teams.
Indian football rivalries too have deep roots. The East Bengal- Mohun Bagan derby brings the city of Kolkata to a standstill, in spite of little to no promotion.
The ISL provides a novel concept where fans of rival clubs team up against common enemies. For example, Bagan and east fans unite against their Goan counterparts. This makes for some riveting banter and helps promote the game.