I don't think that's very true. Smartphone-like sandboxing is widely praised for its security and stability benefits, UWP failed due to a lot of other factors (eg. Windows 10 Store, lack of Windows 7 support, etc.)

It wasn't _just_ the sandboxing. It took an unreasonably long time for MS to loosen restrictions on "sideloading" (read: distributing sandboxed apps outside of the Microsoft Store), and the deployment story for line-of-business applications was abysmal for years.

I'm not saying the AppContainer sandbox is perfect, but I suspect it would have gone over a lot better if the early distribution story for UWP had been less of a disaster.

It has been available since 2018.

Which is why Microsoft went around and is incrementally merging Win32 and UWP, including sandboxing for Win32.

Don't cry victory as you would be quite surprised how Windows will look like in 5 years or so.

I don't think anyone rejected it because of sandboxing. It is a new API that would only work on windows with that installed. Learning something completely new for a niche target is not very enticing. Also, if you can write something to be sandboxed, there is a good chance it can be a web page instead.

Sandboxing also needs to come from the other direction.

Having programs be made to be sandboxed defeats the purpose. What is needed is the ability to do contain all of a program's files in one place and isolate the access to the file system with permissions for other resources.

Can you elaborate? What is UWP and why did devs not like it? All the critique i see with a quick google comes from game devs.

Developer push back first started with windows 8 with fears of lockdown. Valve's CEO was the most vocal because it looked like MS's end game would be to crush steam.

Microsoft didn't help matters with the 99 dollars developer fee - not high per se but in an existing free for all operating, pushbacks would happen.

Microsoft basically said to use this shiny new crippled toy, you must use our store and pay money.

Microsoft also fanned the fire when they announced that only one metro browser was allowed. That is you could only use the metro browser of your default desktop browser. Others would be disabled

For me as a user I hated/hate, UWP, metro and all it's incarnations because:

UWP apps are slower than regular apps. In the early days they crashed a lot. They wasted desktop real estate with too much whitespace. Initially they were not resizable like normal windows application. Oh... The hidden settings menu sucked.

Microsoft also consistently undermined the new format by limiting UWP to the latest operating system. Metro apps couldn't run on Windows 7. Most Universal apps made for Windows 10 won't work on Windows 8.1 and lower. Some wouldn't even work on some Windows 10 versions.

For developers, having to maintain multiple versions written with different API's for "one operating system" is crazy.

UWP apps are basically unusable without mouse or touch screen. Almost all the shortcuts we know and love don't work.

This flat UI nonsense that makes it difficult for users to detect the active menu or even clickable items was started by Microsoft with windows 8. Google and Apple take the credit cos Microsoft failed with mobile.

So it has little to nothing to do with sandboxing.

If you believe in such a thing as a Windows way, then UWP was absolutely not the Windows way of doing things. Windows developers, used to the Windows way, had only one reasonable answer.

So they thought, hence why Project Reunion is making clear what was already slowly happening since 2018, exposing UWP model in Win32, including sandboxing.

In a couple of years every Win32 app will think it still owns the OS, while they are actually playing on their little virtualized OS, using the same pico process model as WSL.