Re: It isn't like they are mandating its usage, or blocking those third party password apps
Quoting myself from two years ago: "There used to be several virtual assistants until Apple bought what became Siri, for example, but then they were banned for replicating iOS functions. Time-based blue light reduction apps existed until Apple added Night Shift. One of those app makers, F.lux, pushed hard to be reinstated and insinuated their IP was stolen."
Regarding Apple Maps, iOS 6 did in fact ban 3rd party Maps apps for several weeks from launch in September '12. Apple approved a standalone Google Maps app in December. There was a lot of finger-pointing between Google and Apple at the time. Apple finally allowed third-party nav apps into Carplay in iOS 12, only 4.5 years after Carplay launched with iOS 7.1.
Regarding Spotify, Amazon Music, et al., signing up for subscriptions is not done in the iOS apps so as to avoid paying Apple a cut of revenue.
A few citations:
https://www.pcmag.com/news/flux-to-apple-let-our-blue-light-app-in-the-app-store
https://www.lifewire.com/get-google-maps-ios-6-1999194
https://www.theregister.com/2012/09/25/google_maps_on_ios6/