Due to inflation in German in the 1930s, money was less expensive to burn than wood.

Inflation. In Germany after the last war, it was possible to pay 50 million dollars for a nickel cup of coffee, and 35 million dollars for a $35 suit of clothes. This Berlin woman, realizing that fuel costs money, is starting the morning fire with marks “not worth the paper they are printed on”. — taken before 1935