"Do you want to allow example.com to send you notifications" is way more understandable to a layperson than "do you want to allow access to WebGPU" or "do you want to allow access to your graphics card". Especially because they would still have access to canvas and WebGL.

Permission prompts are a HUGE user education issue and also a fatigue issue. Rendering is widely used on websites so if users get the prompt constantly they're going to tune it out.