The main reason why they are in the shape they are in now is... they are poor.
Thier construction methods are a result of that. Like a good part of central and south america, most houses are built out of masonary. Its what they have locally( so it cheap) the prob is they don't use rebar to reinforce it. Rebar its not cheap. When the ground moves, masonary cracks, rebar stops that crack from growing.