The big problem with that is that you end up using different browsers on different platforms (IE10/11 for Windows, webkit for Linux and MAC) which is a bit problematic to support.
LCUI doesn't seem to rely on a specific browser but still remains fairly small so that seems pretty good.
To be fair, it's not that bad (I have made a couple of apps based on the webview) - IE11 is a rather decent browser supporting all the niceties from CSS3, flexbox etc. It's not that different from making layouts for web pages, when you have to support IE11 anyway. All the IE11 pitfalls are covered on stackoverflow, so it didn't feel like wasting much time to make windows version of the app look exactly like linux or macOS.
LCUI doesn't seem to rely on a specific browser but still remains fairly small so that seems pretty good.