HN... where people go to complain about both companies requiring access your email, and companies requiring you to be able to block other companies from access to your email. I don’t get it.

Exactly! Which is as it should be. Way too many websites take for granted that they can do anything with the email addresses provided, including sending spam by default or with no way of opting out. With Sign In with Apple, if they don’t get in my email, that’s because I don’t want them to have it. Then, their poor marketing practices are irrelevant, which actually makes me more likely to create an account on their website.

Many apps also don't want to have the hassle of securely managing user login details.