Where are all the teachers?

Today I met with a gentleman who will be working with another education NGO in southern Cambodia. He has some background in language education, but no real experience teaching young learners.

Again, I wonder, where are all the teachers? Why aren't excellent, trained teachers coming to the developing world, rolling up their sleeves, and helping out? Many school districts have programs that allow teachers to take a year (or sometimes more) off without jeopardizing their tenure or benefits, so why aren't more coming over?

Perhaps it's a simple matter of advertising, maybe teachers don't know just how much impact they could have working in the developing world. Maybe NGO's, like many politicians, think teaching is just something that happens if you give a somewhat intelligent person a textbook and put them in front of a room full of kids.

I just find it hard to believe that in a profession where people are here for their passion and not their paychecks that so few of them are willing to come to the developing world.