This is a good question, and there are very few n=large enough surveys to point to any single cause, but the biggest one is that almost 50% of Internet traffic

This is a good question, and there are very few n=large enough surveys to point to any single cause, but the biggest one is that almost 50% of Internet traffic in India is on UC Browser (from Alibaba) that has very robust ad blocking (which consumes less data than Chrome while browsing). You should expect this to change as Jio becomes more widespread. Disclaimer - I led the India section of this report.