Yes. I know of companies that run mainframe emulators purely to keep using the existing COBOL codebase that was written for them.

They go to that level of weirdness because replacing the existing codebase would not only be much more expensive, but would introduce a great deal of risk that they aren't willing to take on.

A transpiler would not really address the needs of that sort of company.

It's a mix of both, I know that some companies do make a good living writing transpilers to languages like Java or C#. But it also require lots of business knowledge to keep track of the changes so you're definitely right in that aspect.