Because I like and can work with the subtle cultural differences found among fantasy European-like nations.
If you can offer up some detail on the differences between the various African nations, I may include them in my world. If you can't, well, then why are you complaining that I don't?
Or, you can use AEG's Theah...the game world used for 7th Sea...also known as Swashbuckling Adventures.
Britain = Avalon
Ireland = Inismore
Scotland = The Highland Marshes (I like Caledonia better)
Norway = Vendel (They also use Vestenmannavnjar)
France = Montaigne
Spain = Castille
Italy = Vodacce
Germany = Eisen
Russia = Ussura
China = Cathay
Arabia = Empire of the Cresent Moon