I think because fast food is food that has been prepared and distributed to consumers to ease and fast. To save time, which can be eaten immediately with the current social conditions that require life hurry.
I think that fast foods are foods that are prepared to sell to consumers for convenience and time savings, which can be eaten immediately. For today's society who live in hastily.
I think that fast food is the food preparation up sell to consumers for convenience and fast, saving time, which can be eaten immediately. The present social condition, suit to live in a hurry.