The guiding principle in the Apple world goes something like this: If your entire app is really just a feature that should exist in a 1st party app, Apple will probably implement it eventually.
The iPhone comes with a 1st party email app, but many people prefer 3rd party apps. Same for calculators, weather apps, podcast players, music players, password managers, calendar apps, etc. In another comment in this thread, I linked to several articles that were critical of Apple for not including a menstrual cycle tracker in their Health app. Some 3rd party apps filled the gap for a while, but it seems like it was really a feature that lots of people wanted in the 1st party app. You can call it abusive if you want, but others might say that Apple was answering the needs of its customers. If the 3rd party apps provide better functionality (as they often do... see the examples I listed above), people will continue using them.
The iPhone comes with a 1st party email app, but many people prefer 3rd party apps. Same for calculators, weather apps, podcast players, music players, password managers, calendar apps, etc. In another comment in this thread, I linked to several articles that were critical of Apple for not including a menstrual cycle tracker in their Health app. Some 3rd party apps filled the gap for a while, but it seems like it was really a feature that lots of people wanted in the 1st party app. You can call it abusive if you want, but others might say that Apple was answering the needs of its customers. If the 3rd party apps provide better functionality (as they often do... see the examples I listed above), people will continue using them.