Offer your thoughts or opinion on the input financial query or topic using your financial background.

Why don't banks allow more control over credit/debit card charges?
The other answers touch on why having two-factor auth or some other additional system is not worth it compared to simple reactive systems (cancelling lost cards, reversing fraudulent charges etc), but it should also be noted that this goal can be achieved with a method similar to what you describe.  My bank (TD Canada Trust) has an app (I'm on android) that gives you a notification immediately after your card is charged (even test charges like at the gas station).  It's really simple, does not slow down authorization, and makes fraud detection super easy.  (I'm sure some other banks have similar apps).