Good question! We actually asked Apple exactly this when appealing the AppStore de-listing. How come others can require an account and we can't? What was it about our app that made us have to spend the engineering effort to add a guest login (this was a disingenuous argument that I advised against, since we deliberately spent engineering effort to require the login)?

Their response, not the exact wording since it was over a decade ago, was along the lines of: "1. We're reviewing your app, not theirs, so what they can do is irrelevant. 2. Your app core use case clearly functions without an account as evidenced by the previous versions having full functionality not requiring an account."

1. Is a standard Apple reply when you compare your app's treatment to others'. Everyone gets this when they bring another developer's app into the argument.

2. Called our bluff and is pretty hard to argue against unless we changed something core to our backend such that it now requires an account. Even if that was the case, I would expect Apple's response to be "change it back".

Throughout the whole exchange with Apple, I had to be Devil's Advocate, since I advised against the change to require an account from the start, being apparently the only person in the company who had actually read the AppStore guidelines. Nobody listened to me, of course.