Supply chains cannot be upended and moved quickly.
Getting quotes from a supplier can take up to 6 weeks. Then there is tooling manufacturing, depending on complexity is anywhere from a few weeks to 6 months. Or you can ship your tool from your old supplier if you own it. After all that you still need to test and validate the product they are delivering and then ramp up production.
It would take a 2-3 months minimum to move suppliers. By the time you’ve finished this situation might be over and we are onto the next global issue. What are you going to do in the mean time?
Side note It is a false belief that the Chinese cannot manufacture items that are of “good” quality.
They will make it to the specifications that you give them. iPhones are made in China and I don’t think anyone in their right mind would say that an iPhone feels like a low quality product. (In a physical sense)
The biggest issue you will face with the Chinese is them secretly changing the production method to save money for themselves while charging you the same which can cause issue with the final product. But even that can be controlled.
Edit: Also where is all this spare manufacturing capacity going to come from?
Iphones aren't great quality. Didn't they have big issues with them bending a few years back lol. Also the screens crack if you sneeze near them to hard.