Yeah that'll be why (for ref I've actually architected and built something similar to what you're referring to for a product you may have used). What they've done is still over kill though. The first thing someone should've asked is "do we really need this feature?".

None of my cards are saved by a site when an out of the box Google solution does the same thing backed with biometrics. That app can't compete in that feature space and only exposes users to security risks. I'm betting that costs them millions of dollars to implement and then has cost at least a million to maintain so far all for something to expedite a payment process that could already be expedited whilst also introducing tons risk on their side and a degraded and frustrating user experience.