Printed floursacks, (and feedsacks) were a tradition beginning in the great depression, but lasted into the 1950's. It is estimated that by the early 1940's over 3 million women and children were wearing some version of a printed feedbag garments.
Not only were flourssack designs simple, so was the concept. They were used as a promotion to sell more flour because the bag, or sack that the flour was packed in could be reused to make clothes. One of the reasons for there being thousands of different flour sack designs was the idea that the shorter the time that a particular design was available, more designs would be used. Women wanted more fabric designs and would therefore help drive demand for the flour.