Actually that was because most states require that when a vehicle's high beams are turned on, auxiliary lights must be turned off.
Because of the variations in state laws, Ford found it easier to build every car with this feature.
There are ways around it-I know that on TCCoA they have a kit available that will not only increase the power of your headlamps, but will also set up the lighting system so that when you turn your high beams on, the foglamps (and the low beams on the 89-95 Birds/cats) stay on.
Tony Poole