They did—or at least, are trying to. The issue is Apple is saying, based on unwritten rules, that Netflix is allowed to do it, while Hey isn’t. And that’s the crux of the problem
> if an app is a way to exclusively consume content purchased elsewhere, like songs or movies or podcasts, they don't have to have in-app purchases.
According to apple an exclusive email client is not classified as a reader app and so they are forced to offer in app purchases. The guidelines are super confusing and in my opinion pretty crap but it's not a case of favouritism or giving special exemptions to Netflix for example