The first cause is saves time.It is convenient and fast.Then,it is suitable to living rush of society nowadays.A fast food restaurant can eats immediately and delivery because it isn't takes a long time.Moreover,so many people choose to call to order a pizza or hamburger at the work.In some families, the parents work that may not have time to cook.So, it is the choice of parents and children and popularity that makes it easy to buy and versatile.