This is fairly straightforward: If I open my application grid/software menu and see programs, when I right click and choose Show Details, I should not see "Sorry! There are no details for that application." I completely understand if it's a third party application I've installed. Not Zorin's fault, not Zorin's job. If, however, it's something that was added to my system when the operating system was installed, I should get a store page if for no other reason than easy uninstallation.
I wanted to update LibreOffice, and was using the version Zorin put on the system when I installed the OS. It couldn't find it, so I had to take to the command line and use apt list and guesswork to find the relevant packages.* Somewhat more egregiously, the tool to upgrade Zorin isn't in the store, such that older versions need install it with a command line and newer versions can only remove it that way. Likewise, the post-installation tour can only be removed via the command line. I don't need that forever.
Adjacent is that some useful things like Zorin's boot repair tool are absent in the store. I know it exists only because I stumbled on a command line in a help article. Why not put this in the store where someone who needs it can find it? (this is boot-repair if anyone sees this and wants to install it with apt.) What other gems exist that just don't turn up when searching the store?
*The components of LibreOffice were in the store and uninstallable that way. The reason it didn't turn up for me was that I used the actual "LibreOffice" icon, which is basically a launcher/recent documents finder for the main applications.
I don't know if it is listed in the Store when you don't have installed it but there would be Synaptic. It is APT in a graphical Interface - maybe not the prettiest Interface but when You search for Packages or want reinstall something or uninstall, it is a good alternative to the Terminal.
Because of LibreOffice: Yes, the Starter is an Extra. When install a Component - even only one this lands automatically on Your System. Uninstall this one seperately isn't possible as far as I know. It will be uninstalled when You use the Terminal Command sudo apt purge libreoffice-common, but this Command deletes the whole LibreOffice Installation.
Zorin doesn't control the store or the store pages, but I understand the frustration. It has always been an issue with Linux, where you have so many ways to get a package installed.
Sure they do. They don't control the Ubuntu or Flatpak content, but a default Zorin configuration also adds their repositories. For example, search the store for Zorin and select the Send Feedback app. It's very specifically a tool for sending feature requests and bug reports to Zorin's devs. If you look under the install button, there's a dropdown with only one option: Zorin OS. If you search for Lutris, the dropdown has two options: Flathub and ZorinOS. (Presumably, they wanted a version they were sure would be there, since they reference it in their Play Games page.)
They can host the things that are otherwise absent on their own repositories, same as they did these examples, since they're making them available via apt anyway.