The problem is that they can't be customised to whatever the UI/UX team dreamed on their PowerPoint,Photoshop,Sketch,Figma,..... drawings, expecting platform capabilities like on native GUIs.<p>Thus even if supported, they don't do those cool UI/UX workflows sold to clients, and that is how we still end with a div/css/javascript soup, or back to Flash like approaches, now that WebGL/WebGPU/WebAssembly has brought that tooling back into the Web.