This makes sense because the authors were comfortable writing apps this way. At least they started it on a stack that has the potential to be multi platform. I see way too many nice / stylish apps released as OSX only.
I don't think if you plan ahead it would be to disaster to maintain. We have tools like QT or Skia that help you create native cross platform UI-s. I agree that the dev experience is a light-year ahead with CSS+JS, I've done it before, but once you go down that road, it's close to impossible to switch without a serious rewrite. This is not necessarily a bad thing, but something to keep in mind.
