The author’s purpose in citing those who are repeatedly unemployed during a twelve-month period is most probably to show that

there are several factors that cause the payment of low wages to some members of the labor force

unemployment statistics can underestimate the hardship resulting from joblessness

recurrent inadequacies in the labor market can exist and can cause hardships for individual workers.

a majority of those who are jobless at any one time do not suffer severe hardship

there are fewer individuals who are without jobs at some time during a year than would be expected on the basis of monthly unemployment figures