An embedded webview gives you more control over the browser chrome (as in UI), extensions, cookies, etc. It also gives you a shim into some filesystem/OS APIs that a regular sandboxed browser page wouldn't have. It gives you a predictable HTML/JS renderer that you control, instead of blindly hoping that your user will happen to have a compatible browser.

Still, webview UIs are a lazy alternative to actual native apps. I don't like them either, but not every org can afford to hire native devs and write 3x-4x the UI code.