Many people forget that when Japan first started producing cars they were so bad at it some models didn't even operate in the rain. Or that American steel, originally, was supremely subpar to British steel. Its about doing whats best for the country - and having some foreign entity control a good portion of the commerce in the country (especially when it is so easy to build your own) is not a good idea for an emerging economy.
Remember, also, that Jumia will have the same control over market that Amazon does which is immense power and why the United States is considering limiting Amazon's power over the market. Basically, if Jumia begins to not only control the market but participate in the market as well it will be bad for these small nations.