I was part of the MUMPS community back in the 1970s and was the principal author of several documents that provided an executable specification of the language syntax and a guide to implementing globals efficiently, given the systems of that era. (I didn't write any MUMPS code that found its way into production.)
MUMPS was initially developed for the 18-bit DEC PDP-7 in the late 1960's, where memory and disk constraints were severe, and processor speeds were a tiny fraction of today's slowest devices. Early MUMPS programs were limited to 1k characters, so every character counted, with most variables being 1 character long. Globals were done as a hierarchical "database", such as X(1,5,Z), again for space-saving and for efficient retrieval from the extremely small and slow disk drives of the day. MUMPS programs were interpreted, not compiled. With these constraints, comments were exceedingly rare, since they used part of the 1k, and slowed down the interpreter, which scanned every character.
As a computer scientist, I was appalled by certain features of the language, particularly the ability to change a running program by executing a variable. That's a security nightmare, since you could effectively read a string (stored as a global or input from the console) and then execute it as MUMPS code.
Here we are, more than 40 years later, and many of the major medical information systems are still running code that derives from the original flavor of MUMPS. Meditech and EPIC Systems are major vendors of medical information systems, including software for electronic health records, mostly developed in MUMPS. The much-overpraised VA electronic health record system is also MUMPS-based. As with any other production application, it's very difficult for a new vendor to come along and displace an incumbent, particularly if the conversion process is highly complex, as is the case here. As a result, there's no practical way to update these systems, other than rewriting them from scratch for modern languages and systems, something that is unlikely to happen anytime soon.