Why do Amex and Discover keep sending me cards applications?

They are on a fishing expedition. They screened 1,000s of profiles to see which ones might be potential card holders that they can sucker into getting one of their cards. It doesn't mean you will get a card if you apply. Your credit profile doesn't show that you have the financial resources to pay the card balances (a job, some kind of income). That is exposed when or if you actually apply for the card. There's no guarantee that you'll get the card.

Take note: Your score will take a minor hit anytime you apply for credit whether you are approved or not. So do not apply for a loan or credit unless you have every intention of taking the loan or credit.

No, it does not mean that you are already approved. It means the exact opposite. It means that you are not already approved.

It means that they want you to fill out an application so that they can decide whether or not to approve you. If you were already approved, then they would not need to send you an application.

All it means is that you are on a mailing list getting solicitations for credit cards. It does not mean you are approved for anything. Minor children and even pets get those credit card solicitations.

You meet their criteria for a potential customer and they are hoping to interest you in adding their card to your wallet. Typically they pay one of the credit bureaus, such as Equifax, for the names and addresses of people who meet their criteria, and then they send out the ads.

No, you're not automatically approved, but there is a high likelihood that you would be.

Securely destroy the applications.