GMO Frankenfood made in labs hasn't been proven safer than regular meat in peer reviewed studies yet.
Eating all plants like potatoes in The Martian have to take multi-vitamins as well. It is boring to eat the same thing each day.
McDonald's has farms so that it can sell a $1.48 McDouble cheaper than a $6 salad. If plants cost more money, why eat them when meat is cheaper? Ever tried to price plants in the veggie section? They cost too much, but you can buy a frozen pizza for $3 which is cheaper.