This is more because there isn't an incentive (monetary or otherwise) to do that. When Flash gaming was big, web-based games were on the desktop but web games never took off on mobile which got pretty much all the audience they used to have on the desktop. Instead mobile games are largely native (or at least in app form).
I agree that it took many years for HTML5/JS to reach Flash's capabilities (and some stuff like easily swapping around SWF files is still not as easy to do) and i dislike how Flash was forcibly killed instead of losing its popularity "naturally" (though it being proprietary technology instead of some open standard or at least an open source project help its murder considerably), but the reason you do not see Citadel-level stuff on HTML5/JS has more to do with not being much of an incentive to do something like that than the technology being able or not (demos like After the Flood[0], which has as much gameplay as Citadel yet it shows more advanced rendering techniques - you can even look yourself in the glass reflections :-P - show that it is technically possible).
Citadel is from 2011, but this doesn't matter, the point is that you can do stuff like that on the web.
> doesn't work on my Vulkan aware mobile GPU
If the GPU is Vulkan aware then it might be an issue with your browser, though from [0] it looks like only Apple's devices do not support it - which wouldn't support Vulkan either, so i'm not sure why you'd bring that up.
I agree that it took many years for HTML5/JS to reach Flash's capabilities (and some stuff like easily swapping around SWF files is still not as easy to do) and i dislike how Flash was forcibly killed instead of losing its popularity "naturally" (though it being proprietary technology instead of some open standard or at least an open source project help its murder considerably), but the reason you do not see Citadel-level stuff on HTML5/JS has more to do with not being much of an incentive to do something like that than the technology being able or not (demos like After the Flood[0], which has as much gameplay as Citadel yet it shows more advanced rendering techniques - you can even look yourself in the glass reflections :-P - show that it is technically possible).
[0] https://playcanv.as/e/p/44MRmJRU/