You seem to be confusing UI with actual features and infrastructure. GarageBand and Pages have always been a bit of a pill to use, and each update just replaces one frustration with another while they shift around where to find functionality (if you can find it at all) instead of how it functions in totality.
Tell me what features are missing from, say, the iOS photos app that iPhoto has. And also tell me why you believe these missing features cannot be included to a Photos app for Mac.
And more importantly, please describe what is so fundamentally different from Photos and iPhoto.
RAW file processing, faces and places database management, batch change of metadata, exif management keyword management and smart albums etc.
There are tons of things the iOS photo app doesn't have that iPhoto does. Some of it is pretty processor intensive. And a lot of that stuff you wouldn't want in a simple iOS based cloud browser.
I mean you don't want to manage some if the intricate under the good stuff on an iOS device, especially if they take a lot of storage and processing power.
Maybe the cloud could solve that, like handle the faces database.
But all sorts of things like managing and merging import events, renaming them, a more robust file management system all require more robust software.
Local management is actually the most jmprtant part of it and photos will entirely be cloud-based.
Photostream which is only part of iPhoto at the moment is inherently broken the way it's handled. You stand to lose your entire photostreams due to the way it's handled on macs at the moment, and I don't trust that they can fix that and trust my entire photo library to a cloud based system.
For example, whenever you transfer a photo to a shared photostream, it actually makes a copy and adds it to the stream. Fine. But when aperture needs to rebuild, it can lose track that these photos actually belong to the stream and identifies them as orphaned files. It suggests you delete them. And if you do it removes them from all the streams.
Would you trust your ONLY copies to a syncing system like Photos? Where one device
Or piece of software decides a file doesn't belong and then it's gone EVERYWHERE?
I don't.
As for explaining why it couldn't be done in a photos app for mac? Impossible, because of course everything is possible. You could just dump every single feature from iPhoto's into photos. But just because you could doesn't mean you should (jeffgoldblum.gif).
I think that shared browsing and basic editing should be separate from local and heavy file management.
The question, though is probably more should they turn iPhoto into photos, and push everyone who wants a "truck" photo management tool towards aperture?