Why do we still need to install stuff? Why can I run webpages just fine without installing anything? Installation shouldn't exist, at least not from the user's point of view.
Because the tools we currently use (mostly programming languages) are too insecure to allow you to run any random code from the internet (that has full access to all your computer resources). And most users would be incapable of keeping proper security practices needed in this case.
Installed software is considered to have a distributor, ie. a legally responsible entity that can be punished for any shenanigans.
I believe this is an outdated model and that with better tooling we could do what you envision.
Then perhaps the distinction should be the programs called 'Windows installer' type in Explorer that TFA is talking about and not a blanket inclusion of all software that isn't ASM written on the device running it.
The only cases I can think of are games (which are huge and GPU-intensive) or stuff that deals with filesystem a lot (dev tools, torrent clients). Those areas are still anemic in browsers. Other than that no reason.
It more or less doesn't in MacOS, and has NEVER really been a thing.
While there ARE some tools that require a more invasive "installation" process (e.g., VMWare Fusion), the overwhelming majority of Mac software is installed by just dragging the application bundle into /Applications.
(App bundles are just special directories, more or less, so you're moving more than just the file, but it presents as a single thing.)
To remove an app, you just drag that bundle into the trash.
This usually DOES leave behind things like local user data or preference files, but those are inert text files and don't impact perf or machine behavior in the long run. Users typically waste more space on cat pictures.
The tl;dr is that "installers" and "uninstallers" only exist because Windows needs them. I have seen MANY MANY FOLKS come to the Mac and be VERY confused by this. "But you NEED an installation process! This can't work!" Nope. Windows needs an installation process.
I joked, in the 90s, that despite all the monopolistic chicanery from Redmond, their real lasting awful legacy would be the degree to which they lowered people's expecations about how computers worked, and I stand by that.
(Something else not needed on sane systems: "clean up" software. If you don't litter the file system with files when you add a program, you don't need special utilities to run that shit down and delete it later.)
It's a bit weird to act as if macOS didn't have installers and uninstallers. For one thing, there's the App store. And then, probably most developers use something like homebrew.
What you describe works for a specific kind of app, the ones that can be easily sandboxed and don't have shared dependencies.
Sounds like you don't understand that Mac world very well. That's okay.
D/ls from the store do what I describe above. The overwhelming majority of Mac apps going back to the pre-MacOS / OSX days work exactly as I described above.
Load a sufficiently large and complex spreadsheet in Excel vs Sheets and you'll have your answer. Sheets will freeze and Excel will open in seconds.
There's also a feature gap that Google will probably never close, because why bother if you can't load the volume of data those power users are working with in the first place.
