How come ford is planning to build cars in Mexico?

Ford has been building in Mexico for a long time.
Look at the first digit of the 17 character VIN on your vehicle, any make, If it is a "3", it was assembled in Mexico (from Chinese parts), if it it "1" or "2" it was assembled in the US and Canada respectively, (from Chinese parts).

Why not?
A more educated and savvy work-force leads to a better, more efficient job!

Cheaper labor costs.

Because we hammer them too hard here.

The Big Three build cars in countries around the world, to include Mexico and Canada. Generally these plants are to get around import taxes in foreign countries. That is why the Japanese build Toyotas, Nissans, Hondas and Subarus in America, same for Volkswagen. Very few cars are shipped internationally anymore, some countries require right-hand drive which Detroit is not prepared to change its assembly lines to accommodate, but the Mexican line does. American manufacturers would be at a competitive disadvantage in other ways as well. Few countries have the safety and fuel economy regulations that America has, so building a car to American standards makes it more expensive than others in that market. Some markets require engines to run on alternative low octane fuel, so they need special engines made and lighter weight bodies.