> One example is copy-paste, which doesn't always work as expected in Linux.

Give example.

> Another is things in OS X, such as deep Spotlight integration with apps, and a unified scripting and automation language between apps.

I am sure KDE has it too.

One time I needed a shortcut for concat-ing 2 images, and I was able to get the son-of-a-bot Gemini to script me a .Desktop file + .sh script which added it as a context menu option to Dolphin. I didn't even know it was possible. I am sure even more automation should be possible with D-bus.

> You can also use links between most apps

Android has this, and I think it can cause borderline security risks. Anyway its' not as important these days when everything that could use a deep link from another app is a react app in browser anyway.

> And drag and drop files and stuff onto and between apps, etc.

I need it maybe 2 - 3 times a day. I can always use Paths and paste them in the file picker. Its never a deal breaker.

I'm talking about why hundreds of millions of people use desktop environments, not why you in particular should use a desktop environment. You are of course free to make your own choices.