Mostly logistical - but also about lowering the bar to use the card to buy things online; things like verified by visa and other solutions are catching on though, but in most cases [I have seen] they are not mandatory.
It has been seen (by the cc companies) making it easy to use (not using "too much" security) means that everyone and their mom can use it, and if there is a problem - reimburse the person and if possible freeze the transaction to the seller.
Also as long as things as paying via the phone etc is possible using a cc then that makes a solution with keys a lot harder to implement.
The fact that a cc company will reimburse is also one of the security measures for the end users, they know that they will get the money back if the cc number is stolen - as for instance Schneier says in the book "digital security", he gives a example of buying a palm plot and the fact that the name of the payment site was different from the store.