Why do banks take time to move payments from one country to another?

Ram Pillai is on the dot! Mostly it is time-zones and the money moving through direct banks or correspondent banks which takes times. Not to mention, most receiving banks like to keep the money a day or two before they hand it over to the client (earn float, cost of funds is near zero!).

You might want to read up on Faisal Khan's answer to What exactly happens when a wire transfer is made? How does the money travel from the sender's account to the recipient's account? How much time does each step take? What regulatory measures are in place, if any?