I think IPO changes the company from founder's interest to shareholders interest.When your company starts selling shares the amount of people buying, can vary due to the type of business you are in,your competitors and the company's management.Remember the dot com crash,it was disastrous as everyone wanted to become rich quickly.
So,when you consider the scenario of startup s in India, most of successful ones like Flipkart are just copies of companies like Amazon.If the IPO goes wrong, then your company will face it's death easily due to lack of sufficient cash.as most of the startup are not in a position to take this risk,they dont offer stocks quickly.