Mostly because of credit card fraud. Credit card numbers are constantly being leaked like crazy, and criminals have a hard time testing them by hand. So they r

Mostly because of credit card fraud. Credit card numbers are constantly being leaked like crazy, and criminals have a hard time testing them by hand. So they rely on automating fake purchases on small shops so they can verify the number is correct. Another common thing is criminals selling products via non-legitimate shops for very little to "launder" those card numbers. After a customer pays, they buy the proper product on a proper shop with another stolen credit card number. Any investigation takes long enough for those people to just disappear and get away with it. We gotta fix credit cards as much as we need to fix the web.