I read that the gestation period can be longer than 14 days (up to 28 days if I remember correctly). In addition, a good majority of these cases are asymptomatic or with very mild symptoms. This may explain a much higher spread than assumed by the numbers. It can also explain that a large number of cases, this time symptomatic, are highlighted after so long. Consider that the population in India is much younger than ours (I'm Italian)* and therefore this has allowed the virus to go unnoticed for a longer time. This is my guess obviously.
Even assuming a gestation period of 28 days, the virus had all the free run to do its thing from January to March 20th in India, so why it didn't? That's a mystery. If most people were asymptomatic back then, then why did the virus specifically choose the time of March end to start showing symptoms in its hosts across the world (not just in India)?
* https://www.indexmundi.com/india/demographics_profile.html * https://www.indexmundi.com/italy/demographics_profile.html