Wow, I never thought VC++ and MFC are this extensively used in demoscene groups.
The choice of platform had to take the majority into account: most people didn't want to write demos that ordinary people couldn't watch. The opinion of programmers was not the most important factor anyway, simple because most people in the demoscene were not programmers -- there were musicians, graphics artists and all sorts of non-productive members besides.
The demoscene was really born out of cracks/intros/loaders which means its origins are C64/Apple/Atari etc and assembly language.
It was also the first to support extended memory in MS-DOS.
I don't understand your comment. There were lots of PC demos in the late 80's.
Demoscene started on the 8bit world and as the PC world started focusing on MS-DOS, so did the coders.
As one of the goals of the demoscene was to see which groups were able to push the machine to the limits while minimizing the amount of code, the used algorithms were worth gold and thus kept secret.
So open source was a foreign word in the demoscene universe and everyone was happily coding the latest demo, instead of getting alternative OS to run on their PCs.
Demoscene is also nearly entirely Windows-only. It's a good platform for games, and thus for demos. Plus, culturally, demos are about as closed-source as you can get, so there's this natural repellent force between the hardcore Linux zealots and the hardcore demoscene geeks.
VC++ is much easier to work with than GCC on Windows (and I'm not talking only IDE but API support, debugging, binary size, etc)
Also, video driver support is best on Windows.
But of course, demos are made for Linux/OSX as well. You can try them on Wine as well under Linux, it's worth a shot.
Pardon, I meant the PC Demoscene. Don't want angry C64 demosceners here.