These are countries with low unemployment, but also low pay, so sex work appeals as a lucrative (and less boring) alternative.
Many of this women were single mothers and the money was sent home. Few, from what I could tell, used drugs. And all were very strong people - I think that line of work requires it.
So in some parts of the world prostitution is just another job.
Is this the same everywhere? Unfortunately not. And I'm sure the industry as a whole is filled with tales of sorrow.
There are advocacy groups out there campaigning for sex workers' rights, staffed by sex workers and former sex workers, and I would think that if the profession were really so bad for independent providers then groups like this either wouldn't exist or would have a very different character.