Most manufacturing plants place highest value on training and retaining the people who build their core/high end products.
I have always assumed that the CA factory focuses on training and retaining people to build the more expensive USA core guitars while the Mexican factory builds the trendy "soup of the day" guitars that change and change and change.
If you are going to rapidly change less expensive products then you want labor that is less expensive.
As Fender diversifies their offerings they are making some things in Mexico that they can charge more for.
"The rock and roll business is pretty absurd, but the world of serious music is much worse." - Frank Zappa