I think in most cases the American companies have discovered the problems. However, products get qualified at the beginning of production, with agreements about component use. There has to be some level of trust, and most companies don’t assume their supply chain contains immoral scum. And remember, I’m sure the contract was done before the latest problems showed up.
When I started in the computer business it was common practice to do incoming inspection on parts arriving at your factory. Today that’s very rare, since component suppliers know to ship parts to a given quality standard. Unless you are dealing with health critical items, you can’t afford to inspect everything on the assumption your partners are untrustworthy.
I suppose the only solution is to boycott Chinese made products to force companies to source elsewhere. That should convince the Chinese government to put these scum up in front of a firing squad, which will eventually fix the problem.