Wrong assumption. Ming trading with SEA continued during the 14-16th century, trading Ming porcelain and other goods for spices, teak, ivory and turtle shell, with archaelogical finds in Malacca and Singapore. Indeed, the wukou pirates were also large Chinese merchant fleets which rebelled against the trade ban of 1540, which was started against the the threats of piracy and smuggling...a scorched earth policy enacted that reflected Ming China weakened military( a Mongol army would attack Beijing, their capital during this period.)
The revival of her military ended the trade ban, to the extent that a few decades later, Spain would allow a precious bullion run to Manila and half of the silver mined in Peru found its way to Ming shores, creating the famous China trade that would lead to the EIC adventures further east to the Oriental.
Similarly, after a Qing naval ban enacted against Ming loyalists in Taiwan,(where a Ming warlord pirate captured the Dutch colony), the Qing resumed trading overseas, with documentated visits to Bangkok. Indeed, just one year after the founding of Singapore, the first Qing junk called in port to engage in entrepot trade. Never mistake the Canton trade system of protectionism for lack of interest in mercentilism. Indeed, what are the Hong merchant barons, if not mercentilists??