[trapperkeeper74]

In the late 90’s, I helped port a nuclear reactor simulator to Win32. It was around 20 million lines of Fortran and was actively developed by physicists and engineers (none were really software engineers). And, at that time the codebase was around 40 years old. Apart from disabling virtual memory, it worked on winDOwS nearly flawlessly on an COTS PC and ran about 50% faster than the fastest *nix test lab box.

It’s done mostly for historical tradition reasons, and it costs nontrivial time and money to switch.