For 2 reasons. 1st: Ours is financed by Japan with long term loan. 2nd: We value good relations with many countries. Afterall, for complex projects such as High Speed Rail, there are many disciplines involved. Civil, Mechanical Traction, Electrical, Signaling and so on. No need to learn all of them in one go. There are 10+ projects coming up. We will get the technology eventually, voluntarily by competitive bidding among players. A good chunk of our High Speed rail projects are being executed by Indian contractors. They are really learning and gaining the experience.
PS: My employer had the opportunity to oversee some of the domestic contractor's execution based on Japanese specifications. We learned quite a lot.