As someone who frequently programs (relatively) complex biological models, I frequently rely on direct visual feedback. Visualisations can not only help to quickly see the results of my program, but also allows the debugging of strange behaviour. However, such visualisation can really slow things down, and I have therefore always stuck with programming in C with the lightning-fast X11 library.
However, both C and X11 are as dated as they are hard to work with. Moreover, every operating system needs a different compiler for the C code, while support for X11-library is waning. Rarely does a piece of C-code simply run “out of the box”.