ISVs made Windows versions of their apps ages ago when their customers pressured them to because they wanted to move to Windows from whatever they were using before (usually UNIX); this is no different.
Of course they did because at that time they expended huge amounts of effort supporting the various different platforms but when the trend of everybody having their own flavour of UNIX on their own hardware died out in favour of a more standardized x86 PC platform that ended up running Windows for better or worse the ISVs saw the value in consolidating on the one dominant platform. Sure they could have kept spending resources supporting SunOS, Xenix, IRIX, HP-UX, Minix, et al but what would be the value in that?
So the question really is: what advantage does a different OS give them that would be worth the expensive and effort of getting ISVs to make new versions, and of getting your IT department to switch? Well, we can go back in time and ask the very same question of companies in the 1990s, when they all switched to Windows.
Well actually we can't go back in time, perhaps you can enlighten us as to what you think that answer was?
Am I the only one here who remembers a time before Windows?
We had many different very expensive workstations that had different operating systems - SGI systems running IRIX and Sun systems running Solaris for example - then eventually it made sense to just buy Windows-based workstations because they were much much cheaper and more powerful thanks to economies of scale.