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Population advantage is surely having very big impact on IPL popularity but recently too much money is also involved in this all peoples are spending some good amount of their funds into betting, and it's all about good marketing and some good information about these games to peoples.
Marketing is a good aspect, you need to advertise to the general public that a tournament is going on, but those advertisements will only entertains the interest of the fans that already know Cricket. To make the sport popular are they doing anything and i doubt they really care about that.
Even gambling is banned in subcontinent but still many insiders and peoples involved in this business specially in India which is also having big impact on other side in Pakistan these things are not in better shape they have some strict laws and economy is also not good as India, so they will be not popular as IPL but can still live at second spot with their finances. If they improve quality and have some better facilities, then it's going to be more interesting for viewers and fans of the respective franchise.
In illegal Cricket betting India is the hub with all the corruption cases over the decade and buying information about the match, the bookies try their best to get their information through any means and some of the player fall for their smartness.