Well, the fact is that it is much harder than producing an engine.
Building an indigenous engine is a issue of technologies, but building a production line of your own for a foreign designed jet is about technologies, industrial standard, industrial investments, etc, etc.
Chinese can do that is because they have spent 20 years to decode every single part of every Soviet industrial departments they imported in 1950s. They were very familiar with Soviet industrial procedure and standard. And don't forget, that was 1990s, plenty of Russian technicians (not those top group scientists) were looking for jobs, quite of them ended up in China.
India, on the other hand, has none of these.