WHY ARE grim-faced CEOs of American automobile companies, discouraged by the collapse of their home markets, seeking less thrifty customers in, of all places, Japan? What explains the proliferation of "For Rent" signs in the storefronts of our cities and towns--gruesome documentation of the leap in retailing bankruptcies from 12,500 in 1990 to [7,000 last year? Why was the Christmas shopping season a disaster, why are newspapers and magazines getting skinnier as advertising vanishes, and why are banks finally cutting the interest rate they charge on instalhnent credit?