From Theodore Trefon’s book Congo Masquerade:
The colonial system of cantonnage, whereby each village was responsible for maintaining its own roads, was relatively efficient in keeping the roads open, but it was at the price of forced labour and the colonial whip. Europeans during the late colonial period could travel from Stanleyville (Kisangani) to Leopoldville (Kinshasa) in a Volkswagen Beetle in three days. This is absolutely inconceivable today and will remain so for many years to come. (p. 52)
Here’s Wikipedia‘s map of Congolese surface transport. The data on road conditions is nearly 15 years out of date at this time, but my strong suspicion is that it hasn’t improved much, especially in the interior. The trip from Kisangani (northeast) to Kinshasa (southwest) would be more than 1100 miles almost entirely on dirt or gravel roads, or by river.
Google seems to know what it’s doing in this case, because it won’t propose any overland route from Kisangani to Kinshasa.