I always assumed the expiration date on card was somewhat of a holdover from before online transaction verification was the norm. The bank would assuredly refus

I always assumed the expiration date on card was somewhat of a holdover from before online transaction verification was the norm. The bank would assuredly refuse to renew a card that was in default, so the user couldn't just keep using it at merchants that were still using paper slips. Though a new account number is not quite as much of a big deal as it may seem. The issuers publish lists of old->new mappings, so that processors and merchants can update records, and some networks/issuers will accept reoccurring transactions on old numbers, as long as those were started before the number was issued. It's kind of amazing what the issuers and networks will accept.