One other thing that seems powerful is that users that use Sign In With Apple have some guarantee of quality; with Apple using FaceId to authenticate, there's some amount of guarantee that you're not a bot.
Of course they wont. They still want the business and as you've pointed out, these accounts will be in a different customer engagement category. They are almost certainly real people and they a lot of value to marketers, even is you don't have all of their other personal details.