China to some extent also needs foreign workers to fill out workforce gaps. Even if a migrant man doesn't directly contribute to fertility for obvious reasons, they indirectly help by freeing up labor.Where do you propose these foreign brides come from? SEA, south Asian, and some African women may be willing to come but only rural Chinese men are interested in them. If you open the open the floodgates of immigration, I guarantee you Chinese cities will be swamped with foreign men instead.
The root cause of declining birthrate is households working 2 jobs. People always want more, and when your society offers them a lot of expensive luxuries and choices, theyre not satisfied with just 1 income anymore. The only way to directly fight it is by narrowing peoples' minds, reducing their hopes and letting them be satisfied with less.
That's not an option for China, so instead they just have to free up conditions to let people more easily have children. More work from home opportunities, use foreign labor, bring in foreign families/women, normalize hiring maids etc.