Roaches have been on earth since before the age of man, and are something no one wants in their home. Because they feed on garbage, they spread germs from their feet across your home, which can make you ill.
Roach control is difficult because they multiply so quickly, and because if there is nothing else to eat, they will eat each other. Roaches' ability to survive drought, flood, fire, and famine is what makes them so successful as a species.
Over the years, roaches have developed a resistance to many of the chemical pest control methods. Natural roach control methods, while slower, are actually more effective simply because of the way they work.