Recent Blender versions have OpenGL version dependencies and VRAM requirements that aren't supported on a lot of older or lower-end PCs.
For fans of, say, older laptops that have "mechanical" keyboards, or people who only have access to less-powerful hardware, I wonder whether Vulkan will re-enable support for the latest Blender.
(Though the VRAM might still be a problem. As will local rendering of expensive animations.)
GL 4.3 as minimal version most likely means that they are using compute shaders. The GL 4.3 standard is 13 years old though, so it's not exactly bleeding edge any more ;)
AFAIK the entire Blender UI (not just 3D preview) runs on top OpenGL.
I don't know if compute shaders were the reason for the GL 4.3 requirement, but from own experience, having to support different GL versions in the same code base isn't exactly trivial without resulting in a granular #ifdef-mess.
The cleanest solution is to have different backends for different GL versions, but that means a lot of duplicate maintenance effort and code.
But tbh, any cheap laptop made in the last decade should be able to run GL 4.3.
The only exceptions I've seen so far are VMs and the Raspberry Pi.
For fans of, say, older laptops that have "mechanical" keyboards, or people who only have access to less-powerful hardware, I wonder whether Vulkan will re-enable support for the latest Blender.
(Though the VRAM might still be a problem. As will local rendering of expensive animations.)