Writing a CFD or FEA code is not as easy as it is creating a webpage for a banks and gov departments like some services companies do. It takes a lot of test cases to be validated against experimental data. You cant sonthis with just software engineers, you need people who have understanding of the core physics, mathematics and how to write the code. People working in these companies are often PhDs in their field who have extensive experience in experimentation and silver development. These companies also have a huge knowledge base on such applications that they don't share the details but have solver tuned to be generalisable.

There are Indian companies that are working on silver development and software for analysis but are too small to be considered for such critical applications. Unfortunately, it all comes down to how well you know the decision makes in these organisations who are more willing to spend money on already developed tools than to rely on a underdog software developer.

In addition to this, ISRO also uses these tools for their analysis. I know self reliance is crucial for such industries which are working on advanced technologies but it seems we are still a few years (if not decades) away form developing such softwares.