Untold numbers of high paying jobs in the US disappeared as the US lost it's manufacturing base primarily because the leaders of US companies discovered they could vastly increase their profits by manufacturing their products in low wage countries.
The Apple facility only needs 50 highly specialized engineers and techs. Other than some of the admin, security, maintenance and other misc. personnel, that's pretty much all they need. It is unlikely many of the technical people will be found locally.
It is unrealistic to expect US unemployment/underemployment problems to be solved or even significantly mitigated building facilities like this. It is also unrealistic to expect all these displaced manufacturing workers to retrain to become technical workers or medical workers. Even if they did, there's only so many of those jobs to go around.