I'm not sure where you're getting "you can't close apps" from? There's background tasks but that's not a windows store thing? It does work on local accounts, you just need a Microsoft account to use the store. You can sign into your Microsoft account on the store and still have a local account.
I can see the complaint. In an Android or Apple phone, you can't just close an app. Perhaps you can log out, but that would defeat the purpose of having apps that remember everything for easy access. At best, the app is suspended when not in focus; many actually do keep background activity going (harvesting your data, usually) when not in focus.
If that's what UWP apps do, which appears to be the case for some of them, then yes it's a problem for those with any desire for security and privacy. My impression is that a minority of UWP apps actually do that, unlike in phones where the majority do (though the OS in the phone may kill the process after a while, and it's possible to manage background permissions if you dig deeply enough). A plus is that the MS store is relatively clear about what permissions an app is demanding; you have to do a little diving in Android to find everything, and there are often red flags (why does nearly every app demand access to my contacts, for instance?).
As for the point about nobody buying software direct, which planet do you live on? Lots of software is available from the original publisher, and that's where you go for support anyway. I have a couple of significant items purchased from the original publisher, and in Windows if you use open source stuff you pretty much have to get it from the source (not compile it from source, usually, thank goodness).