Look at this screenshot of context menus in Windows 10 https://pbs.twimg.com/media/C2Y6rwoXEAAaQll.jpg:large win32, MFC, WinForms, WPF, Web.. Why don't stick to 1 framework and make it work good, deprecate rest, why have multiple buggy and ugly. If compare HTML/CSS and WPF improvement over last 15 years it is 10000 to 1. WPF could have been great 5 years ago, but I'm not sure it ever will be.
We already know that the Office and Windows teams have different GUI toolkits from reports from inside the company. But there is evidently a lot more fragmentation than just those 2 groups.
What I find more interesting is that Google products are starting to feel similarly fragmented. Project fi, Android, Plus, and Search all look and behave differently. My damn phone gets SMS on Hangouts and the Messenger app, my voicemails come on the phone and hangouts. None of it makes sense.
We can all agree that inconsistent GUIs are bad, but it seems like a problem you have to solve from a top down organizational perspective, which might not obviously align with the business.