To be fair, I think a lot of that has to do with the fact that the countries in Africa have been very influx over its history.
For instance, Portugal was founded in 868.
Conversely, the country that is now the Democratic Republic of the Congo didn't have that name until 1997, Zimbabwe was known as Southern Rhodesia until 1980, and several other countries go by multiple names depending on the language and colloquialism. And that's not even mentioning the various territorial and governmental changes that have occurred throughout the previous few centuries.
In short, Africa has been a land of pretty consistent change and upheaval the past 500 years or so, and people's unfamiliarity with its various countries is bred from that. Whereas England, Spain, etc. have been in business for literally thousands of years now.