It's easy to answer that; let me put it on caps - CORRUPTION.
Most investors are afraid of investing in African countries because of how corruption has terrorized development strategies.
For example, an investor from Country A wants to invest in an African country on a project that requires many background checks or meeting some regulations before they invest. The investor wants to invest $1,000,000 in the project plus registration costs, but they will need an additional $10,000 to buy chai (tea) for the local authorities to make the process faster. Some investors will do that, but others who stand against corruption will give up on investing in African countries and will opt to invest in a European or Asian country where corruption is the biggest crime for a public officer.
Europe, Asia, or western countries will continue developing, while in Africa, we shall continue the same story of corruption.
Big lesson-Corruption starts at home when you tell your kids to do house chores, and you will buy them some sweets or anything they love. The same way you tell African leaders to allow you to invest in a project, and you will award them well.
Let's End Corruption and develop our Africa!