I'll guess that the countries' own western-educated elites suppress its use.
Or foreign aid depends on banning DDT.
In 1962, Rachel Carson published Silent Spring, a book that falsely alleged that DDT was causing great harm to humans, beneficial animals, and the environment. The hysteria generated by Carson and her disciples forced bans on DDT that have resulted in hundreds of millions of human deaths – and human suffering beyond the ability of statistics to reveal.
The campaign Carson launched hit hard at the war on malaria, causing it to falter. In 1967, the World Health Organization changed its goal from worldwide "eradication" of malaria to "control of the disease, where possible." Some 63 participating countries, which had already spent considerable sums on the fight, simply gave up the battle.
A resolution was approved by a large number of concerned scientists at the 22nd session of the WHO Assembly in Southeast Asia in 1969 urging manufacturers of DDT to "continue producing the life-saving insecticide so that they could continue to protect citizens from malaria." A ban on the production of DDT in the United States, they said, would deny the use of DDT to most of the malarious areas of the world. The direct result of such a denial would be "to bring down upon the afflicted countries hundreds of millions of cases of malaria, and millions of human deaths from malaria within the next decade."
http://mitosyfraudes.8k.com/INGLES/Killer.html - An info-rich article by:
Gordon Edwards, professor emeritus of entomology at San Jose State University in California, has taught biology and entomology there for 44 years. He is a long-time member of the Sierra Club and the Audubon Society and is a lifetime fellow of the California Academy of Sciences. He is the author of several ornithological articles published by the Audubon Society and other environmental groups.