Why does China rely on imported high-purity casein despite domestic production?

Why does China rely on imported high-purity casein despite domestic production?
China's casein industry is structurally constrained by feedstock. Domestic production is predominantly based on qula, a byproduct of yak milk butter, rather than fresh milk, which limits quality and yield. Annual domestic output of food and industrial grade casein is around 35,000 tonnes, but much of it is low to mid-tier product. High-purity casein, roughly 5,000 to 6,000 tonnes per year, must be imported, mainly from New Zealand, Australia, Russia, and Ukraine, where fresh milk is the raw material. Imported casein typically commands a price premium of about 28% over domestic material. This quality gap persists because China lacks sufficient fresh milk supply for cost-effective casein production, leaving domestic producers unable to compete at the top end of the market.