An airplane's engine accounts for about 1/3 of the airliner's total costs. Just like the advanced semiconductor chips that power everything today, engines represent sophisticated technologies that China does not have.
The US is the home of modern aviation and has the most advanced engine technologies in the world. With the current US/China hostility, there is no way for the US to bolster China's fledgling plane maker. On the other hand, the C919's extensive reliance on the US suppliers for key parts presents the US government a trump card that it can use at will to nip it in the bud.
...如果中国”拉闸“，拜登可能连擦屁股纸都找不到 :-)
==========================================================================
那就只能用TOTO全自动马桶了。