Why and when is the the "best tool for the job"?

Whoosh

It's an ideal language for creating business reports, which is what it was originally designed to do. It has built-in commands for reading randomly or sequentially from a database and it has extensive report-formatting options. It has other application capabilities, of course, but business reporting (especially complex reports) are its sweet spot.

They don't refuse to pick COBOL, they refuse to consider COBOL.

They even forget that COBOL could run on their computers and servers.

That is true for MUMPS too. People overlook what an epic decision they could be making.

The big problem with MUMPS is that as the "Massachusetts General Hospital Utility Multi-Programming System", it does not work well for development in other states. There's been some experimentation with using it in Wisconson, but a W is not an M.