More than a decade ago, MS used to kind of have that, and mostly consistent at the architecture level, but I think it was only by chance (win 3.1 programs still

More than a decade ago, MS used to kind of have that, and mostly consistent at the architecture level, but I think it was only by chance (win 3.1 programs still had all their legacy dialogs, including open file), because they just did not have had the time yet to implement 1000 different graphical frameworks for example, or to evolve dozens of ribbon interfaces from various unrelated teams. Now it is nothing else than an absolute mess: Win32 programs are very different from UWT stuff (and not just the drawing of the control, the whole interaction model is completely different), and you've also got layers of unrefreshed designs inherited from the guidelines (or informal practices) of the day of the version of windows the component was first introduced in, with inspiration flowing from other teams (or even other systems) but with no common technical framework continuously shared between them, so for example Office also has its very own stuff. This is a big difference, and in the end a classical one, in the way companies typically work compared to open source projects (not just open source code, I'm really talking about the whole project being open): in companies teams or individuals just don't collaborate as much, because projects are often extremely closed even within the companies, with all kind of access rights. And also some app team might want to support really old OS (who uses a Linux distro of 2009 today? Well, OTOH tons of people are using a Windows version from 2009...) for a few more years and that OS certainly won't add any kind of support for the UI the app guys want, and the app guy might not want to use loads of resource to make their app look neatly graphically integrated in old OSes. In summary, for proprietary stuff, this is an hard problem both at the technical and at the organizational level, especially if you like to change your graphic experience so often like MS does. And now everybody is used to seeing widely inconsistent stuff on the same screen anyway, so old on new / new on old / different on different cases will remain, I guess. Plus converging UI from vastly different devices is also a hard problem in itself, and UWP is actually not bad at it -- but the price is obviously that it must be irrecoverably different from old Win32 programs.