When it comes to malt, it must mention its predecessor, barley. Just as many people don't understand that hops are a kind of plant, many people don't know that malt is a germinating barley. After germination of barley, the enzyme that produces the starch can convert its starch into fermentable sugar. These sugars are converted to alcohol through yeast and they have what is called a beer. Since its birth, beer is the main raw material of barley.
There are many reasons, such as ease of germination; The growth conditions are not harsh, adapting to various climates; Low price and low cost for brewing; It's not a staple food, it's made of alcohol and style and so on.
When it comes to staple food, there have been numerous prohibition laws in history to solve the problem of insufficient food. In China, for example, when food is in arrears, the government will restrict or even prohibit wine making. Abroad too, is very famous in Germany the beer purity law of a large part of the reason is to restrict the use of other staple crops are born for wine, were later interpreted as German "rigorous" is drunk.