Apple’s default applications, such as its Mail application or Books application, cannot be rated by users – insulating Apple software from the risk of negative reviews or low ratings.
Specifically, Apple designed the iOS App Store in such a way that users are not allowed to submit a rating (like a two-star or three-star review) for certain Apple applications.
Thus, Apple immunizes itself from a form of competition its competitors must all face – effectively making Apple the only software developer whose apps are listed (usually as the first result) without any negative feedback or comments.
Apple chose to eliminate rankings for its own applications in order to protect those applications’ placement in the App Store.
According to the WSJ, Apple has intentionally made decisions about App Store design that benefit Apple’s own applications over competitors.
For example, an “Apple app, Podcasts, previously averaged a 1.7-star rating before reviews [for the application] were eliminated, according to Sensor Tower. It appears No. 1 in a search for podcasts.”
https://www.wsj.com/articles/apple-dominates-app-store-search-results-thwarting-competitors-11563897221
Apple avoided taking steps that would improve application quality in the App Store at the expense of its own offerings. For example:
“Phillip Shoemaker, who led the App Store review process until 2016, said Apple executives were aware of Podcasts’ poor ratings. Around 2015, his team proposed to senior executives that it purge all apps rated lower than two stars to ensure overall quality. ‘That would kill our Podcasts app,’ an Apple executive said, according to Mr. Shoemaker.”
https://www.wsj.com/articles/apple-dominates-app-store-search-results-thwarting-competitors-11563897221