The reason for that being is because it would discourage people from buying imported manufactured goods so they would buy domestically produced manufactured goods instead.
It makes foreign goods more expensive. That allows domestic industry the luxury of charging more for their goods because now foreign goods are more expensive.
Among blue-collar workers, a structural shift in China's economy, from ... The impact is pronounced in many of the hundreds of towns that ... As a local boss explains, “People simply won't pay more for a pair of socks.”