MUMPS (har har) has it's origins in the medical world so there are a lot more people versed in mumps in that world that have domain expertise regarding hospitals but you'd hope that that chapter of the Cambrian explosion in programming was closed by now and that someone would come to their senses and would say: absolutely no more new development in MUMPS. (And 'Mapper' for that matter.)
They were dead-ends 30 years ago, they're not magically going to be better in 2015. Of course it would be hard to get rid of 1.8B euros using any other available technology so maybe that's were we can find part of the answer of why this happened.
Maintaining MUMPS code is an interesting exercise in pasta consumption, the language more or less dictates it.
See also: http://thedailywtf.com/articles/A_Case_of_the_MUMPS