Question: Why isn't C/C++ called platform independent like java when the same source code written in C/C++ can be made to run on different operating systems by different compilers, just like JVM is used in java.

Isn't different compilers and JVM doing same thing and achieving platform independence.

Answer: 
It's not the language itself that is platform dependent. It's possible to compile both C and C++ for JVM, but it's not very common to do so. [Compiling C++ for the JVM](https://stackoverflow.com/q/4221605/6699433)

In the same way, it is possible to compile Java for a specific target instead of JVM. [Compiling java source code to native exe](https://stackoverflow.com/q/28249838/6699433)

But Java and JVM are both designed to work together, so that combination is very natural to use.

C is designed to be very close to the hardware. There's not really a reason to use C if your target is JVM. Then use Java instead.

In theory, you can compile ANY language for ANY target, as long as the target is turing complete.

Sidenote: Don't write "C/C++". They are completely different languages.
The role of JVM in the independent platform is that it acts as a virtual processor. when we used c/c++ to compiler different processor converts the source code into a different binary pattern that's why there are not platform-independent.