Even basic things like reading and writing files from the filesystem are obnoxiously difficult in a pure browser or PWA environment. Storing state in general is full of enormous pitfalls and eccentricities, like 50mb limits for some browsers or just completely random total deletion of all app state at the browser's whim.
Fine, but these are proposals. We want something we can work with today, something that we have the power to hack on that will expose new systems we come up with to HTML/JS, and that is the niche that Electron-like systems fill really well.