With the new Music app in macOS Catalina, which retains most of the music functions of iTunes, but sloughs off the other media kinds that the previous app managed, there is a change in the way the iTunes Store is handled. In some cases, users won’t even see the iTunes Store.
In early betas of macOS Catalina, the iTunes Store was visible, but in recent betas it did not show up in the sidebar of the Music app if the user was signed into Apple Music. That seems to be the default now: if a user has an Apple Music account, they won’t see the iTunes Store. You can display it, if you wish, in the Music app’s Preferences, on the General pane, but if you’re a streamer, you won’t see it by default.
You’ll note that in the screenshots on Apple’s macOS Catalina preview pages, the iTunes Store is not visible.
The iTunes Store is certainly not going away, but Apple is considering that streamers don’t want to buy music. This isn’t the case with the TV app, which retains the tabbed navigation bar of iTunes, to show one tab for Library, and four other tabs to entire users to find new content. Granted, the way we consume music is different from movies and TV shows, but this is a clear sign that Apple is betting on streaming for music, and rentals and purchases for video content.
It’s interesting that, while Apple has made the interfaces of the four apps that replace iTunes (Music, TV, Podcasts, and Books) very similar, two of these apps retain the tabbed navigation bar: TV and Books. And these are both apps where there is more content to purchase than to stream. (Obviously, all podcasts are free, so there’s no need to have a marketplace in that app.)
In the Books app, I think the tabs don’t make sense. There is one for your library, which is logical, but there are two store tabs: Book and Audiobooks. I think it would be better to have a single store, because there are a lot of people who buy both ebooks and audiobooks, and splitting them can make it harder to find which options you have.
As for the TV app, that has the potential of quickly becoming bloated. There are tabs for your library, then for Watch Now, Movies, TV Shows, and Kids. The problem with the TV app is that it aggregates not just your own content, but potentially channels, networks, and services that you subscribe to. And that leads too bloat. But the very nature of these disparate services makes it hard to do otherwise.
Update: Commenters have asked about searching with the iTunes Store disabled. When you search in the Music app, the search results show three tabs: Apple Music, Your Library, and iTunes Store. If the iTunes Store is disabled, then you only see the first two tabs; if you don’t have an Apple Music subscription, then you only see Your Library.
You can, however, go from Apple Music to the iTunes Store, even if the latter is disabled, by clicking the … button next to any item and choosing Show in iTunes Store. However, searching only Apple Music will not find items that are for sale in the iTunes Store and not available to stream.