how can they when we dont use them for technical study... So first cut a person's legs, and then condemn him for not running the race
Again you missed my point. If you want an Indian language to be the language of technical study especially Sanskrit, then the ship has long sailed. And don't blame it on the British. Sanskrit had no new research for centuries, may be even a millenium. That is the reason why we see BS like vaastu and kundali and fake 'rationalists' who explain the 'science' behind those. For centuries, India was ruled by kings, Hindu and otherwise, whose court language was not Sanskrit.
Sanskrit was opposed as a lingua franca after independence for a simple reason that we would be reinventing the wheel. We would be in a tragic situation where the illiterate would be struggling to learn a tough language which was not their and worse, the educated people, the intelligentsia would be learning their alphabet in Sanskrit instead of teaching other students. So our scholars would have been the pandits, basically only a subset of Brahmins who still learned Sanskrit. We are in dark enough age with the kundali BS, we would have sunken to even a worse situation. The obvious corollary being that the upper castes only would dominate education(even worse than it has been). No wonder sensible and educated people opposed Sanskrit.
Whatever you think of 'technical study', I will quote a German professor joking: "... English is THE language of science today, except probably for the French who won't agree..."(his emphasis). And this guy is from the land which gave us Einstein and Godel, whose path breaking papers were originally written in German. I can't emphasize this enough; even with people like Einstein and Godel, English is today the language of science.
You may be right if you say, ancient Sanskrit texts should be studied and understood for any scientific findings which we might have missed. But to revive a language because it was once the greatest sounds like paying off a debt. When Sanskrit was THE language of science, people from all corners of India did rush to learn it. But now, it is past its sell by date. It is too costly to attempt what you are saying unless there is a huge social change. We are already being forced to learn three languages.