That is a side effect of the UNIX culture, because the hardware doesn't matter as long as you have C and POSIX.
Even OpenGL and audio APIs made it so that most of the time the cards you have plugged are irrelevant.
Being a old timer, which also has spent quite a few time with Amiga users/devs back in its golden age, it took me a few years to realise, that in what concerns desktop graphics programming, macOS and Windows communities are much more welcoming than UNIX focused ones.
You see this quite clearly on macOS, those that came from Mac OS days (pre OS X) focus on UI/UX and the whole experience as a dev taking advantage of an unified software/hardware stack.
Those that came from BSD/Linux just use CLI tools as if they were in any other UNIX.
Which is one reason why the demosscene never thrived on GNU/Linux.
I think it has less to do with C and POSIX, and more that Unix from day one was multi-user, you can't have someone "bitbang" hardware when there are multiple users accessing.
Also, i think perhaps you conflating issues here.
While sure they may be more interested in the GUI (though you will find plenty of TUI programs in the Unix world, and even some in Windows that has been inherited from DOS) the newer generation is less likely to be interested in the actual hardware beyond that it works to run their precious "apps".
And IMO the demo scene were largely "dead" by the time Linux come on stage anyways.
This because the fixed hardware models of the C64 and like were being supplanted by the mix and match PC, where the only commonality is the BIOS and the CPU ISA.
Even OpenGL and audio APIs made it so that most of the time the cards you have plugged are irrelevant.
Being a old timer, which also has spent quite a few time with Amiga users/devs back in its golden age, it took me a few years to realise, that in what concerns desktop graphics programming, macOS and Windows communities are much more welcoming than UNIX focused ones.
You see this quite clearly on macOS, those that came from Mac OS days (pre OS X) focus on UI/UX and the whole experience as a dev taking advantage of an unified software/hardware stack.
Those that came from BSD/Linux just use CLI tools as if they were in any other UNIX.
Which is one reason why the demosscene never thrived on GNU/Linux.