Among many others, I think chief among the reasons for Africans backwardness in this area are poverty, ignorance, superstitious traditions and politics.
As stated above, an impoverished person, comparatively, is a disillusioned person. There minds are focused on immediate survival and may have very little time to analyse matters beyond that or, sometimes, even the brain power to think through that as they may just be survivors of a malnourishment related disease or other.
Poverty also means less formal education which limits these people's sources of information as they seek and read. So they remain ignorant. When someone does not know better, they just don't.
The entrenched spiriticism traditions of Africa, fit in very well with the religious superstitions from the west or Arab lands. It is an easy cross over as opposed to the leap into skepticism.
Then politics come into to take advantage of the scenario. Politicians fall over each other win church leaders as they seek political power through the so called democratic elections.
In my country, some thieving former president 'declared' the country a 'christian nation' some twenty years ago but to date even the other politician who objected nonsense then, are can not dare say they would remove such from the preamble of our constitution as they know the crazed pentecostals will not give then a vote.
It is a rough ride but all we can do is chip at the stone little by little through helping those close, our children for starters, to see the light. The battle is won at home level. Once kids survive the superstition, then they are free. For adults, it is tricky. Most just cant change.
I think that breaking the tie between material wealth and god is one thing to do.
In my studys of peoples around the world who ever has the most stuff and or military power is assumed to have gotten their position of power because of a more powerfull deity, so it makes sense to convert, if one believes in deitys. the western christinanity and knowledge has the seeds of its own denial.
I.E. use the examples of disease or lightning and thunder 500 years ago no one knew what caused them and they were attributed to god / gods, witches spell etc. now everyone knows what causes them, therefore the reason for everything else that we dont know right now will be discovered!!!
This is the million dollar question!
I think it is about trying to open up the debate, encouraging a broader discussion about religion (to move it away from fundamentalism), to expose religious fraud, to provide alternative explanations for the supernatural. I'm starting to believe that what we need to do is not attack but to gently put forward a scientific understanding of the world and normalise it.
How do we do this? That's the tricky part. I show friends skeptical documentaries and intend to have a movie night, and try to get other progressive organisations to show them and discuss the issues. I blog and tweet presenting a different view of the world but also to challenge the excesses of religion. I hope this helps to take away the fear of questioning. We also need to make interventions in the media - get on radio chat shows, reply to news articles, letters to papers.
Ultimately, we need to hunt down a group of people who think like us and feel as passionately about this.