Except Apple then moved the App Store over to their OS, yet no one is criticizing them here as much as they do Windows. Oh, and they still support side loading, like Windows.
The industry doesn't care what Apple does with OS X because it doesn't have enough market share to matter. If Apple decides to close OS X, there will be moaning, but no developer of significance is going to die because many 3rd-party Mac applications are available for Windows as well. OTOH, when it comes to non-mobile PCs, Microsoft essentially is the market, and 3rd party Windows developers exist because Microsoft allows them to. If Microsoft decides to close Windows, the 3rd-party developer market would be fundamentally altered in a way that would force a good portion of the market out of business.
When I lose the ability to not install applications without the Windows Store, come talk to me - but odds are, Microsoft would lose a lot of business if they went with that model.
Microsoft is being pushed by market forces harder than they've been since the early 90s, and they are under pressure to perform. Microsoft has the desktop world by the balls right now, and the only option that users have is older versions of Windows (and consumers that buy retail PCs don't realistically have that option). As Microsoft's market share erodes and falls below the levels needed to generate antitrust scrutiny, you can expect them to begin reigning in their ecosystem, particularly since they've already taken the steps needed to do so.
It's certainly not without precedent. Windows Vista eliminated the ability to run unsigned hardware drivers, and with Windows RT, Microsoft has done the same for applications.
As I mentioned in my original post, as an end user, Linux doesn't have much (if any) immediate benefit to you. However, software developers whose business depends on software sales need to take the long view, and Windows is not moving in a direction favorable to their interests.
Hell, I remember having app installation GUIs for yum or any other repository on Ubuntu 5 years ago.
Linux package repositories provide a convenient way to install software. You're not forced to use them, and you can install software from source, a customer installer, or however you want.
Software markets like the App Store and the Microsoft Store serve to monopolize the distribution of software, with the vendor serving as the gatekeeper. If that gatekeeper doesn't like you, they can effectively lock you out of the platform with no recourse. In addition, while I can't speak for Microsoft's conduct, I know that Apple has used their App Store monopoly to prevent the distribution of apps that are against their interests.