MUMPS was originally developed in the 1960s for use on minicomputers that had maybe 64KB RAM. At the time it was a lot more important to keep code size small, hence the single letter commands. Readability wasn't a concern then but it sure looks like a mess today.
Imagine harder. It was an enormous improvement over assembly language. Not so much for the basic coding but for the portability and built-in persistent data structures. MUMPS has an excellent "NoSQL" database built in which is a pretty good fit for a lot of healthcare use cases.
