3.1/3.11 was what was bundled with almost all store bought computers at that point. Most people weren't out there grabbing up NT 3.51 licenses to do dev work. There were quite a few OS/2 devs around. The hardware support for NT was just craptastic. NT 4.0 got a whole lot better.

The thing for many people was, Visual Basic was the entry point. Or Turbo Pascal in my case. But it was DOS based, so it didn't really matter to have a real 32bit OS under the hood.

I'm a bit curious why you'd never consider Ubuntu for development. At the end of the day, it's all the same if you're doing C/C++/Python/Ruby/Node/PHP. Then again, I've been a Linux fan since Redhat 5.2. (1997ish) I had to use IRIX at work (Graphics animation stuff for TV) and even though it was "unixy" I rarely had to fight the typical unix battles. Same for AIX at my next job... dealing with cell masters and all that crap was an IBM thing, not a unix thing.