The main practical reason is funding sir. If a project needs 350 Cr. IR allots 17 Cr. in a year. At this rate you can calculate how many years it takes for completion. Often said by ministers, IR needs approximately 1 lakh 25 thousand crore to complete all the projects. Planning commission can specially give 25 thousand crore per year for total 5 years, if they really need to improve the train service. Rather, government spends every year on petrol, diesel subsidiary for around 1 lakh 80 thousand crore. Imagine, that much money goes by just burning oil, nothing remains. If government can think wise, things can change. (But there are lot of politics involved behind spending government money on oil products and reasons are beyond the scope of the present post to discuss them).