The majority are connected to pieces of research equipment where upgrading to a more modern windows version isn't possible because the manufacturer won't write drivers for the newer OSes, and replacing the whole lot involves sums in the millions or tens of millions
abudhabi: I have one sitting beside my workbench right now that I use for weird old software that wants Windows XP and hardware access, occasional data recovery, and other nostalgic retrocomputing stuff. Doesn't go online though :)