Volunteering in Costa Rica

I don't understand why people volunteer in other countries especially in fields for which they have no training. I recently had contact with two people who volunteered in Costa Rica. One was a 19 year old female college student that was not studying nursing who was volunteering in a medical clinic. The other was a 35 year old male computer scientist volunteering in building housing. The woman paid something like $700 for the volunteer experience and I don't think that this included airfare. She knows very limited Spanish and spent her days doing unskilled activities. The average hourly wage in Costa Rica is $1.00 per hour for most skilled jobs such as clerk, and blue collar jobs. She could have hired a group of  Costa Rica nursing students for 50 cents to a dollar an hour to work in the clinic and when she left they would still be benefiting from the experience and she could have spent her time at the beach and everyone would have made out better. The computer scientist could have provided computer training which could be helpful such as training local people to rebuild thrown away computers from the U.S. to create jobs. Rather than working as an unskilled labor which can be had in Costa Rica for under 50 cents an hour. When both of these people returned to the United States they could have volunteered in New Orleans which has people as poor as or poorer than anywhere in Costa Rica.