I received an invite to “apply now for Apple Card” and I was denied. Why would that email be generated to me if I was going to just be denied?

The email was part of a marketing campaign. The department that sent the email had no access to your credit records. They may have had access to other demographic information that lead them to believe you might be interested in applying (you own a lot of Apple products, you live in a certain zip code, you spend a lot of money in the App Store). But, they would have no way of knowing if you would qualify once you do apply. And that's good. You don't want marketing departments to have access to your credit files.

Why do I get flyers in the mail asking me to sign up for meal delivery services? Or to buy a new car? I don't believe I can actually afford a new car. But, the local Toyota dealership doesn't know that. They just hope that if they send enough fliers to enough people, some of them will buy a car.