Finder and Notes are artificially and arbitrarily designed to hook into iCloud first and refuse any convenient synchronization with other cloud platforms. It is pretty easily argued that these apps are designed like this to upsell Apple iCloud subscriptions, not because it's easier or smarter to do that way.
Similarly, Safari isn't clouds and rainbows either. It serves the same purpose IE did back in the day; furnish a "premium" experience that is deliberately irreplaceable and intertwined with the OS. We saw this with the push notification API, "Add to Homescreen" functionality and so many other places where Apple dragged their feet and refused a featureset that would enable competition with native apps. This is a hell of their own making, Apple can leave any time they want by acquiescing to app publishers the same way they did on Mac.
Similarly, Safari isn't clouds and rainbows either. It serves the same purpose IE did back in the day; furnish a "premium" experience that is deliberately irreplaceable and intertwined with the OS. We saw this with the push notification API, "Add to Homescreen" functionality and so many other places where Apple dragged their feet and refused a featureset that would enable competition with native apps. This is a hell of their own making, Apple can leave any time they want by acquiescing to app publishers the same way they did on Mac.