The issue is that most flyers rely upon an agent to rebook them. Most don't know the airlines routes and hubs. That is the key to getting re-accommodated either same day or next day-knowing the airline's route system. Otherwise, you're reliant upon an overworked, probably burnt out agent that isn't going to scour Reservations to look for potential re-routes, such as connecting through a non hub airport or taking a double connection. For example if you're flying from Miami to Chicago on AA the agent might only look for space on that particular route or only using a hub to connect, which might not be for another 2-3 days.