Ask HN: How do SaaS companies continue to charge my replaced credit card?

My credit card expired earlier this year. I received a new one with the same number but a different expiry date and an updated PIN code. Most of my subscriptions continued without a hiccup. That is kind of explainable since the card number was the same. What blew me away was what happened after I lost the card and got a new one. Again, most of the subscriptions continued charging the new card as if nothing had happened! How?! I logged into my SaaS accounts, they’ll prompted me to update my expired card. BUT, they continue to charge my new card without knowing its details. What kind of dark magic / next level fraud is this?