Why is it mandatory to drive with one foot instead of two?

So I am 19 (I know a little late to be starting but I first drove when I was 15 and I kinda know a little and I figured better late than never). So my dad owns a parking lot with long areas of plain pavement with seemingly endless amounts of straight with no people or cars and he lets me since I was around 15 drive his Honda civic around his parking lot and around the long streets. At first he told me that I could only drive 15. He showed me the ropes and taught me how to use blinkers and shifting ect… But today he told me that I cant use both feet because it is dangerous and the driving instructor will fail me when I go for the test. I asked why and he didn't really have a simple answer. He kinda in a round about said that he didn't know why and it was just the rules. I question it because 1. I tested it and it takes around 1.289 seconds to take the foot off the gas and place it on the brake and plant it. It only takes about 0.289 seconds to just put down the left foot if it is already there. Sometimes when I would go to brake with one foot it would accidentaly hit the gas pedal. That never happens with two feet because they each have an assigned position. 2 feet, 2 pedals. It just simply makes more logical sense. I don't get the logic behind using one foot. Can someone please help me. I don't mind doing it I just want a reasonable answer. Someone told me that if I panick I will stomp both feet down but that is rubbish because I would still stomp the one foot down on gas
Added (1). So regardless id still crash if I panicked and planted the foot down. Which I never do when I panick but I have never gotten into a proper accident yet. Thanks for the help anyone.

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