Why do Windows programs need special installers/uninstallers? Why isn't this handled by Windows itself?

Windows has had an installer as an OS component since the late 90s (called Windows Installer). As a sysadmin I'd prefer apps use it. Many application developers do not. It's maddening. (Doubly so when Microsoft themselves don't use it-- newer versions of Office, Teams, etc. Microsoft suffers from too much NIH.)

I get unattended installs and uninstalls "for free" when well-behaved applications use Windows Installer. Patching is included, too. Customizing installations is fairly straightforward.

On the developer side it has historically used a very quirky proprietary file format (MSI) with a fairly steep learning curve and a ton of "tribal knowledge" required to make it work for all but the most trivial cases. (Though, to be fair, most installs are the trivial case-- copy some files, throw some stuff into the registry, make some shortcuts.)

Worse, it allows for arbitrary code execution ("Custom Actions"), at which point all bets are off re: unattended installs, removal, etc. Some Windows Installer packages are just "wrapped" EXEs (Google Chrome, for example).

I've packaged a ton of 3rd party software as Windows Installer packages. It's an ugly system with lots of warts and legacy crap, but if you need to load an application on a large number of Windows PCs reliably unattended it's decently fit for purpose.

There is reasonable free and libre tooling to generate MSI packages from plain text source (the WiX toolkit) and it can be used in a CI pipeline.

I assume the Here in NIH refers to an individual team, not MS as a whole.

Teams is entirely NIH https://github.com/Squirrel/Squirrel.Windows for updates to the Electron app.

I would use winget, but MS made it weirdly hard to run as a script on multiple computers, it installs per user, because... who knows.

So still using chocolatey