The "concepts" are different. iPhone is a mobile device, usually with minimal local storage. Mac is a computing platform, usually with plenty of local storage. The default functionality on each is optimized for the platform being served. Also, it's not "redundant" for most users, because iCloud Music Library contains iTunes Store purchases AND songs added by the user from other sources (often more of the latter). For you, it may be only iTunes Store purchases, but that's not the norm. Therefore, showing your purchased songs is not the same as having an iCloud Music Library (for most users).
On a Mac, you need to add a song to your iTunes library in order for that song to appear in your iCloud Music Library (if it's not already there). That makes perfect sense to me; I don't necessarily want every song I've ever purchased to be in my current music library. I can also REMOVE a song, that I no longer want, from my iCloud Music Library. It remains a purchased item that I can download again from iTunes Store, yet it no longer appears in my iCloud Music Library. That's what you are describing; songs that are past purchases, but do not appear in your iCloud Music Library.
On an iPhone, you may want to play a purchased song, but not store it locally (to save storage space). Not everyone has an iCloud Music Library, which is part of subscribing to iTunes Match and/or Apple Music, so Apple provides the option to stream purchased items as a benefit of buying from iTunes Store. You can't stream other song you added to iTunes library from other sources (unless you have an iCloud Music Library). You said you have your lCloud Music Library not enabled (on iPhone), so it's like you don't have one.