You've also probably never seen a dispatch centre have to authorise every transport and tell them where to go. However, that's what we do when processing a transport request (remember, you're technically playing the role of a 911 dispatcher). The transport system isn't "realistic" clearly, so a vehicle/person to automate this part of the game and automatically transport prisoners is just a feature for better efficiency and improved gameplay for us!
The only thing a officer will do is likely tell dispatch where they are going w/o the authorisation. So I completely agree with you. On a somewhat related note the "sheriff unit" needs to be changed to police supervisor or somthing.