I work in the pharmaceutical industry. One of the most important and possibly expensive regulatory activities we perform on our control systems is extensive software qualification/ validation.
Bearing in mind that most of our control systems are on closed networks (no internet connection) changing operating systems not only means complete local re-validation, but also involves the supplier often having to write bespoke software to make their applications run on a different OS. It is exceptionally time consuming and doesn't even guarantee everything will work correctly afterwards. During this effort, our plant may also not be available for drug production.
It's not a particularly good place to be, with obsolete OS and software, but the relatively quick pace at which IT stuff is obsolete effectively means we would spend a significant amount of our time not producing life saving drugs. Stuck between a rock and a hard place.