The maps you are looking at are petnird that way for clarity, not the actual route. Commercial aircraft travel is conducted using specific routes between ground based navigational aids. These routes are called Victor Airways. At the time when these airways were set up we didn't have sophisticated electronics or GPS satellite systems. Aircraft traveled from navigation signal to navigation signal. Flight controllers expect aircraft to be on specific routes and specific altitudes to avoid clearance problems (AKA collisions). Aviation industry is slow to change but one day soon we will have commercial aircraft traveling direct from their departure location to their destination saving time and fuel.