For example, their editor has tabs for editor buffers. Cocoa has a static tabbed widget, which has wrong look and odd UX for this. Cocoa also has a tabbed window type, which isn't a widget you can control. I imagine it'd be hard to abstract that away to work consistently with how Windows does tabbed views. I also haven't seen Windows' tabs being draggable, so that would probably need special DIY solution for Windows which Cocoa tabbed windows don't need.
Anyway, I think native UI toolkits are dying. For most people the Web is their most familiar "toolkit" now, and native platforms instead of fighting that back with clear consistent design, went for flat design and multiple half-assed redesigns that messed up all remaining expectations of how "native" looks and feels.
For very contrived example, the cross platform settings panel widget exposes the business API required for settings in general, while the platform specific code takes care of using the host platform concepts to display and manage application specific settings.
While it is more work than lowest common denominator approach, it is still much less than re-inventing the wheel.
As proven by mobile OS platforms, there are still hope for native toolkits.
Lets see how much long the Web will hold, now that the revenge of plugins is here thanks WASM.
