Only raconteurs pick machines for their OS. 95% of any meaningful machine choice is going to be about what software at what price point/form factor it costs to run it.
pretty much that. way back when I started, we sold minicomputers, Datapoint equipment running RMS as an OS, as that was what was running our telecommunications software (this was when AT&T got broken up and there were a lot of CLEC [competitive local exchange carrier] and they needed a way to rate & bill calls. There was little choice so they bought that OS basically to run their business on). There were few options so they paid, we got paid. Eventually as that business went away via consolidation and the cellular started in the same way (those of us who can remember when it was a few $ per minute to call) we converted the software to run on Unix - cheaper servers. We did dip briefly into DOS but the speed and networking was not there. Then switched to Linux but that market was also drying up as everyone was getting bought to get us back to the big 3 or so cellular companies the US has today. And no idea what they run their systems on.
Point being: the OS is rarely driven by choice but by what you actually want to do with it, and in some cases, business requirements beyond the software running on it. Now, having said that, as more and more moves to "the cloud", aka other people's computers, giving you a lot less control over your own software (parallels to the word processor post below) the OS matters less and less, just browser compatibility. Which, though in theory "standardized", does have some variation (recall the IE days, though it is a different company doing that now essentially).
Anyway, I agree with Kilemall that the choice of OS is driven by what you want to run at a price point you are willing to pay, and a a usability factor as well (i.e., you *can* run some Windows with WINE but not always well).
though, counterpoint (sorry!): with PWA (progressive web apps, basically mini-browsers running locally) the OS becomes less a factor. Something MS actually noticed and why Windows is no longer the main driving force there: is all all about the services, the back-end stuff, where the real money, e.g., profit, lies. Though my guess is there will always be bespoke software that is tied closely to the OS to take full advantage of it.
(and steps down off the soapbox lectern)