Low yields means their production can cost more than they sell it for, which is not sustainable. They have to have yields good enough that they can make money, otherwise the government is just subsidizing a give away, which is fine if they don’t export them but wouldn’t make sense if they do.
That's where capitalism-with-Chinese-characteristics comes into play, since the CCP knows it's a capacity they want to get some independence from the government creates incentives to develop it until it becomes self-sustainable.
They have a strategic goal which the government will support while at the same time letting competition do its thing, it's a step above from what other governments used to do with government-backed R&D that would eventually be developed by the private sector into products.
Not sure why other countries aren't adopting this model adapted to their own needs, seems very effective so far. Well, I'm not sure but have a big hunch it's the usual big business blocking it since it'd create more competition in a more level playing field.
China has plenty of money to subside low yields while they improve their technology.
Chinese planning revolves around mastering a technology no matter the cost, then monopolozing the global market no matter the cost, then bankrupting existing foreigner competitors or entirely preventing them from arising in the first place no matter the cost, to only then caring about costs and to start profiting from it all.