They must be assured that they will get to keep the gains they make. This is assured only under capitalism. Another consideration is that prices are not dictated under free enterprise. This price is determined by supply and demand. Therefore customers will not receive the benefits that entrepreneurs would have brought if prices had been left to the free market.
Businessmen decide both what they are going to make and what they are willing to buy.
In economies where capitalism does not exist, there are few suppliers allowed to operate and, therefore, buyers must take what they can get. Take the Soviet Union, for example. During the Cold War, people would stand in line to buy something they did not necessarily want at that time because there was no guarantee that they would be able to get it at a later date. With free markets, entrepreneurs would be free to search for profits. This helps to ensure that there are always products for sale which consumers want.