Actually, the primary cause is inadequate training and licensing of drivers. None of the people who had collisions bothered to try and put the transmission into neutral, or, failing to be able to do that, turn off the ignition altogether. This is the second thing I learned, in regard to how to drive a car. First: what to do if you are not sure what else to do: stop, using the brakes. Second, what to do if the throttle is stuck open and you can't bring the engine speed back down to idle with the throttle pedal: press down the clutch if the car has a manual transmission, and with any transmission, shift to neutral, or shut off the engine (this varies according to make and model). I wasn't allowed to get behind the wheel until I had these 2 things memorized. Then I learned: every time you get into an unfamiliar car, don't start it until you have first made sure you know the brakes work, how to get it into neutral, and how to turn off the engine without locking the steering wheel.
I saw one of the "victims" complaining that first he stepped on the brake and when that didn't help as much as he expected, he stepped on the "emergency brake" and blaming Toyota for having inadequate emergency brakes. Unfortunately, those auxillary brakes that cars have had since 1956, are not emergency brakes, but parking brakes, and every owners manual for every car, calls them parking brakes, not emergency brakes. If the regular brakes are working, but not stopping the car, the parking brake is not going to provide any additional braking. They are simply an additional (cable) connection to the same rear brakes that the regular brake pedal connects to (hydraulically). If the pedal was operating all 4 brakes, but the car wasn't stopping, using this redundant system for activating the rear brakes, isn't going to help any. He clearly was not adequately educated in how cars work, and should not have been licensed.
That said, I still think a computer software problem where garbled signals for the pedal sensor, cause the throttle motor to open the throttle, instead of close it, was the problem in some cases, not floor mats interfering with the pedal. And I still think flying saucers are the reason, in many cases, why the pedal sensors and computer were not communicating properly.