That may be one. But I think another strong motivation is threat of sanctions from US. I don't know the specifics, but even most recently as today, there were news about US wanting India to stop buying oil from Iran or face sanctions (https://economictimes.indiatimes.com/news/economy/policy/no-...).
There is a movie in Netflix called "Paramanu" (https://en.wikipedia.org/wiki/Parmanu:_The_Story_of_Pokhran) that talks about how India was forced by US back then when it wanted to test nuclear bombs. There are also countless other stories including how US tried to stop India from buying cryogenics engine (https://timesofindia.indiatimes.com/india/India-overcame-US-...) and some GPS related incident in the recent Kargil war with Pakistan (https://timesofindia.indiatimes.com/home/science/How-Kargil-...).
This post in Reddit also has some good info: https://www.reddit.com/r/india/comments/27l015/what_fuels_in...