I think, first, the Fiction Publishing, or even Non-fiction Publishing, industry is not as big as it is in the UK or the US.
There they have an industry that has grown over decades and a culture for fiction that has been built and is revolutionary.
There is also the fact that Genre Fiction Writing is not as celebrated in Nigeria... and possibly in Africa, as it is in these Western countries. Here there is a love for Literary "sedate" Fiction and then we cling to past "Masters" instead of building up new ones.
And finally, we have a generation of readers (Nigerian) who want all things "summarized" and for some, it is the penchant to "get it free".
Music and Movies are quick-to-please entertainments and these industries have larger base investors. There are more people delving into both industries than there are steeping their time and money into the Fiction / Non-Fiction Publishing industry.