Just because migrant workers, young and old, and agricultural growers have to work part-time, they have to run at both ends, and they can't finish all the year round, which forms a seasonal job.
There is also a family, the elderly have no ability, and they can only dig in the farmland and look after the children. Some of them are sick, and they have to be taken care of by their wives. Therefore, it is difficult to maintain the economic expenses of the whole family by working alone.