WebGL is not really related to WebGPU in any way. WebGL is almost a strict subset of Gles3, WebGPU is a completely different API, sharing on a few concepts. They're about as related as Java and JavaScript
They're different APIs, but they have similar goals and benefits: expose native-adjacent performance for GPU tasks in a highly cross-platform API supported by browsers and other host software. The original poster was asking "why [vs native graphics APIs]?", and I think the "why" is the same for both.
Also- VSCode is literally an example of a use-case where you might do this in WebGPU, they just didn't