"Is it simply because C++ is compiled into assembly/machine code whereas Java/C# still have the processing overhead of JIT compilation at runtime?" Basically, yes it is!

Quick note though, Java has more overheads than just JIT compilation. For example, it does much more checking for you (which is how it does things like ArrayIndexOutOfBoundsExceptions and NullPointerExceptions). The garbage collector is another significant overhead.

"Is it simply because C++ is compiled into assembly/machine code whereas Java/C# still have the processing overhead of JIT compilation at runtime?" Basically, yes!

Quick note though, Java has more overheads than just JIT compilation. For example, it does much more checking for you (which is how it does things like ArrayIndexOutOfBoundsExceptions and NullPointerExceptions). The garbage collector is another significant overhead.

There's a pretty detailed comparison here.