Apple is not a bank. Apple does not verify cards for adding to Apple Wallet. All verification and authentication is done by the banks themselves. Banks may use the Payment Network Operator (Visa, Mastercard, etc.) for some verification services.
When you attempt to add a card to your Apple Wallet, your iPhone sends data about how you use your device, your Apple Account, and other information that helps the banks and PNO’s verify you, your device and your cards. The information is encrypted and Apple does not know the contents of the encrypted data.
The PNO and bank use the information you send for verification purposes and to reduce the potential for fraud from scammers etc. Apple does not participate in these decisions. If the PNO approves the request, it is sent to the bank for final approval and issue of the dynamic token representing your card. Again, Apple does not participate in the decision process and if a token is not issued, you receive a notification stating to contact the bank. Apple is not informed by the PNO or the bank the reason(s) for the decline.
You may also be interested in the information in this thread in the community.
Apple Wallet Disabled - how to resolve ? - Apple Community