The web browser for UI drawing is only part of what Electron does. It also bundles Node.js and all its APIs, which web browsers don't ship. And Electron also provides APIs for native OS integration, e.g. native macOS menus and whatnot.
Hence web widgets on native UIs.
Oh man I choked on my dinner laughing at this.
That just frames it all up so well.
I'm not familiar with Electron myself, however it's relatively easy to identify which applications are using it.
I know Discord doesn't support using a keybind for push-to-talk whilst the (Chrome) tab is not in focus with their web application whilst their Electron app supports this. Something vital to PTT users whilst playing games.