Osama had a nice $1M compound in a very nice neighborhood in Pakistan. Not everyone lives in slums in Pakistan, India or in many places in the third world, contrary to your assertion. Wealthy neighborhoods suffer the same kind of earthquakes that poorer ones do. The fear of relief agencies is that emergency housing would cause people not to move back to their original towns or rebuild their original housing.
Emergency housing is almost always erected on someone else's land, not the land of the occupants of that shelter and that can cause serious disputes. In India such relocation has resulted in many deaths as rich farmers, who often own the land emergency shelters are built on, hired men to displace the people they see as squatters. As you can imagine, those squatters fight hard to stay because they usually have no place to go. So that's why experienced aid workers might see a problem in the concrete shelters.
-- Bobby G.