Schools Look Abroad to Hire Teachers

On the New York Times website I read an article Schools Look Abroad to Hire Teachers.  This article focuses on schools hiring teachers from other country's.  Most of them work in inner city schools or in rural schools.  In 2005 Baltimore hired 108 teachers from the Philippines.   This year they recruited 60 teachers from the Philippines.  With the bad economy I wonder why there  aren't enough teachers in U.S. to fill these positions.