The remnants of colonialism continue to produce winners and losers economically, with the winners stuck in local maxima where they extract value from the people, but the people themselves see only marginal benefit, and development is stuck at a snail's pace.
As with seemingly everything in life, the incentives for the different players really don't line up. Consumers lose, producers lose, and only a select few middlemen win anything at all.
Economic reforms and cutting down bureaucracy are certainly part of the solution, but "just wait a bit longer" is too. If things continue progressing as they currently are, Nairobi will look a lot more like Seoul by mid-century.