Why has holiday resorts and tourism struggled so much in India despite all seasoned investors heavily betting on it for last few years?

I completely agree with @varadharajanr. In last one year, whenever I checked with my friends and family about their holiday plans, I heard almost all of them have done their booking themselves, whether domestic or overseas.

With more money coming into this sector with starts-ups like OYO etc. trying to go one step ahead by standardizing the customer experience, competition has gone up quite a bit in last one year. So I would expect margin pressure for all older players like Sterling Holidays, Mahindra Holidays etc in the short to medium term.