This is part of the Green Revolution.
To start, we must understand what is the green revolution. It was a period of time when food was getting scarce and people were thinking of methods to grow more food with more efficient ways. And so, under these methods, stuff like the use of machines and the addition of chemicals were implemented.
In short, people have added chemicals such as herbicides, fertilizers and pesticides so that they fruits would be more pest-resistant and would grow much healthily, and more efficiently(Lack of weeds and pests = No competition for nutrients and destruction of the plants). Also, fertilizers allow a shorter fallowing period(Period of time when farmers can't grow plants due to a natural lack of nutrients in the soil), allowing more plants/fruits to be grown per year. More crops + healtier crops = Why people add chemicals.
That is one bad point about the Green Revolution, and it's a risk we have to face with the growing needs of this growing world population. The only way to stop this problem is to find healthier natural alternatives to growing more food, which leads to genetically modified foods which grow without chemicals but aren't really that good themselves either.
Several reasons. For one thing, with the current population, it would be almost impossible to try to feed everyone naturally. It's too slow. Chemicals accelerates growth rate, gets rid of pests, and makes them bigger (thus you've got a larger quantity). And for another, it is cheaper than trying to grow it naturally.
In addition to kyhw's answer it is a cheaper less labor intensive way of getting the three basic growing nutrients (nitrogen, phosphorus and potassium) in the soil. The problem is that eventually most of the trace elements needed for a healthy diet are lost.
to make them bigger and less flawed
the addition of chemicals can make fruit grow unaturally perfect and bigger than normal (though it doesnt taste anywere near as good if it were grown naturally).
These chemicals added into fruit or vegetable growing are very bad for health and it's high time they do something on that as many people are getting effected by this
Saves 'em the bother of adding the chemicals at the processing plant....:-)