Distance is the first. These countries are much bigger than the map suggests and the roads between them are rarely quick. Most multi-country trips here are flights rather than drives, and the regional airlines are worth pricing before you commit to a route.
Season is the second, and it is regional rather than continental. The Sahara and the Maghreb are pleasant from October to April and punishing in summer; East Africa runs on two rainy seasons that move the game viewing around; South Africa has the seasons of the southern hemisphere, so its summer is the northern winter.
The third is that the good parts have no signal, and that is the point. Book, download and confirm while you are in a city, and treat a camp, a park or a desert night as offline by default.