Why McDonalds like picking teens so much?

Why does fast food restaurants, like McDonalds always hire teenager? McDonalds and other fast food chain hire teenagers because they know it’s easier to manipulate by 8 or more hours. For example: this franchise like McDonalds’ would make kids work from 4 until 12. Will only give them a 30 minutes lunch break and the employers have to pay for their own food. They work this time six days a week without any change in their schedule and if they have a change in to work more hours. Many of this teen with these ridiculous hours because they don’t know any better and plus they don’t want to lose their jobs for speaking up.
In the book “Fast Food Industry” by Eric Schlosser in the “Behind the counter” chapter, page 70 paragraph 3 “The management no longer depends upon the talents or skills of workers – those things are built into the operating system and machines. Jobs that that have been “de-skilled” can be filled cheaply. The need to retain any individual worker in greatly reduced by the ease with which he or she can be replaced.” These shows that these restaurant franchises pick what’s easier for them replace and the easing pickings are teenagers. They‘re so easy to replace because they don’t need to have many job experience or if any, the only things they must know is how to press a button and how to put the food on a plate. It makes some sense why McDonalds hire teenagers their just easier for these non-skilled jobs.
I remember when I just turned 16. I got my working papers and when too applied to work for a restaurant around my neighborhood. I went on a Tuesday afternoon and got the job Wednesday morning. I was so happy that I got the job so fast. I thinking in my mind all the cloths that I was going to buy and all the places I’ll be able to go. On my first day I didn’t learn nothing, they only thing I learn was how long I can leave a patty on the stove. It was like that for the next month. That’s all I did for the whole month of November. I’ll go in at 4 and come out at 12, with a lunch of 30 minutes that felt like 15 minutes and my shift ended at 12 but I couldn’t leave until 1 because I had to clean the whole kitchen me and another kid. Also they weren’t paying for staying that extra hour and it was mandatory to say. If not you would get fired, until one night that I was so sick and tired that I couldn’t take and left when my shift was over. My boss called and say “ if you don’t come back then don’t come tomorrow” my respond was “ thank god your are doing me a huge favor.”