Because there is a glut of idle money right now as the first world continues to unwind its debt positions from the financial crisis. Investors are parking thei

Because there is a glut of idle money right now as the first world continues to unwind its debt positions from the financial crisis. Investors are parking their cash in safe assets in droves (government bonds and real estate), so there's basically no safe assets left that will earn a return (perhaps other than real estate speculation) - investors then go on to hunt for riskier investments in emerging markets that will at least gain something, at risk of losing the principal if the government defaults.