There are unfortunately a lot of problems with this – some that matter for the user and some that are more business concerns, but it's sadly not this easy.
- Do users understand the fact that they have not given us their email address? Our email turns up in their inbox after all. Our customers are not necessarily tech-savvy of even that comfortable with email.
- Do users know, months after signing up, that they didn't give us their email address.
- Many users don't actually read information longer than ~5 words unless they're seeking out FAQs or something. They mostly pattern-match to things they know and/or expect.
- Interrupting a checkout flow to explain all of this and capture a real email address will significantly reduce conversion. Is it overall better accounting for the hopeful improvement from Sign in with Apple? Very hard to say, even with testing, and we've tested things like this in the past.
- Will Apple allow it? Open question, they don't explicitly say either way but there's plenty of evidence to suggest they don't want it being done.
> This is not difficult unless you want to make it so for the purpose of raging at apple
There's a difference between raging and critique. I'm critical of what I see as poorly designed systems and policies, particularly where it seems like there are industries/business models that are blind spots to Apple, intentional or otherwise.
Saying that I'm raging at Apple is funny to me because I lead our project to introduce an iOS app at my current company, I've worked at an indie Mac software company, I have used macOS for many years. Hell, I even liked Objective-C. In many ways I'm just yet another Apple fanboy.
Constructive criticism is important in moving platforms forward. Right now, Apple SSO doesn't work for us for well defined UX and business reasons. If those are solved then it will likely align well with how we want to treat our users and we'll likely introduce it.