It's quite impressive how many more lines of javascript and shading is required to show this in a browser, than it requires to bring a window on the screen and show a texture on it using plain C.
With freeglut it's fairly doable to make a version that has wider support than this webpage. Though I definitely prefer this post's syntax to OpenGL.
Not sure if that matters though, given that this is clearly meant as a tutorial for WebGPU, but there's still a ways to go before WebGPU can claim to have broad support.
Additionally, while I tend to bash WebGL and WebGPU lagging behind native counterparts, they are great in one thing, being 3D APIs designed specifically for managed languages.
Also Firefox does WebGL, and if they would have used Threejs or BabylonJS, it would be used instead.
Also, you might struggle to implement glTF and PBR materials with the same line count with SDL_renderer.