You are ignoring costs, expertise, and time it takes to get production ramped up.
Let's say Chinese aluminum makers control the market and puts all other aluminum ventures out of business, and then raises the price until they don't need a subsidy and make a healthy profit.
Ok, so now someone else can jump in the aluminum game. Why would they do that if they knew that China could immediately put them out of business by turning the subsidy back on. Who would invest their money in that venture?
Let's say Chinese aluminum makers control the market and puts all other aluminum ventures out of business, and then raises the price until they don't need a subsidy and make a healthy profit.
Ok, so now someone else can jump in the aluminum game. Why would they do that if they knew that China could immediately put them out of business by turning the subsidy back on. Who would invest their money in that venture?