EU's FDI in India exceeds that of Indian FDI in EU.
India - Trade - European Commission
And how much support has India received? Please name me a single nation that has come out in support of India. While on the other hand, the EU the largest trading bloc and a political powerhouse has already come out with a statement in support of Italy. There is no way the Ambassador will be sent to a jail, not even for a single second. India is well aware of the repercussions of initiating such a move, that is why they have avoided something like this.
I fully agree that the Ambassador implicitly waived off his immunity according to Article 32 of Vienna Conventions when he appeared infront of the court. But realpolitik does not work like this, it works on politics. If an Ambassador of a sovereign nation is jailed, it will setup a very bad precedence and this is why all parties will avoid such a decision.
I hate to be the devil's advocate but India does not has many options to take a strict action against Italy. It is neither the United States or the Former USSR.