Although skin lighteners are advertised by the companies that produce them as an aid to even skin tone and to help hide blemishes, the truth about their use by some women of colour in Africa and elsewhere has to do with a misguided mentality that "White is Right". In other words, a woman with fair (light) skin is prized by many men in their communities more than a brown-skinned or dark brown-skinned woman. This mentality may even jump gender boundaries, but I'm not sure about that.
There is a big problem with bootleg healthcare products from rogue companies and distributor/retailers selling products that are pharmaceutically untested and that cause severe health problems. Here is a link to a BBC News article from November 23, 2004 "Tanzania counts cost of white skin":
http://news.bbc.co.uk/2/hi/africa/4032837.stm
As you point out, white people around the world spend billions of $$$ on products and travel to get a deep tan while these women spend perhaps millions of $$$ trying to get white. A sad irony.