Not sure why you are talking about iOS7 since it was released 7 years.
But anyway the reason Apple doesn't allow for customisation of the home screen is because it adds complexity. And given they are trying to sell to people who are computer and technology illiterate you don't want complexity.
I feel ios7 had lasting negative impact not just on ios, but also general usability on the web. Even Apple back peddled on some of its design decision in subsequent updates.
iOS has gotten already too complex that I don't think avoiding complexity is a strong enough reason for not offering home screen customization.
Compare iOS 7 to iOS 13 and despite the time that separates them, are still very similar, but compare iOS 13 to iOS 6 and the difference is night and day. iOS 7 is still pertinent to bring up when talking about iOS software usability because they changed so much in one version; much of the changes in iOS 7 set the direction for future iOS versions, and for better or worse, those iOS versions have inherited iOS 7's design language.
I always wonder what iOS 13 would look like if they didn't dump iOS 6's design so thoroughly.
Many of the problems started there: the departure of Forstall, Steve Jobs getting so sick and dying, departure of many important roles at Apple and moving Ive to the head of design in the digital part, in my opinion brang the company to a disadvantadged position. In opposite, Google moved quickly and cleanest with Material Design taking Android phones to a new level Apple couldn't reach. Nowadays iPhones are the minority in every market.
But anyway the reason Apple doesn't allow for customisation of the home screen is because it adds complexity. And given they are trying to sell to people who are computer and technology illiterate you don't want complexity.