it seems ridiculous that we have to embed an entire browser, meant for internet web browsing, just to create a cross-platform UI with moderate ease.
Why are native or semi-native UI frameworks lagging so far behind? am I wrong in thinking this? are there easier, declarative frameworks for creating semi-native UIs on desktop that don't look like windows 1998?
It depends on just how "cross-platform" you want to make it. If you came up with another standards-based UI framework that had the same cross-platform penetration of web browsers, then you'll have effectively reinvented the browser. For everything else, you can basically pick a maximum of two: cross-platform, native, and easy.