Why don't American cars last as long as Japanese cars?

My family has owned a Ford Taurus and a Nissan Altima of similar model years. Both cars are still running, but the Taurus has very low mileage (it's a 1999 with only 85,000 miles) and the interior is in horrible condition and the plastics Ford put in have been known for breaking. None of this has happened with the Altima, even though it has more miles. Why?

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