" . . . literally no incentive. . ."
Why?
Japanese foreign policy in the late 19th century rested on two fundamental pillars: 1) Overturning the unequal treaties and 2) Preserving Japan's "line of advantage."
The first is pretty straightforward; it essentially was a manifestation of Japan's desire to stand equal among the Great Powers of the world.
The second was a stark reminder that Japan (until 1920) was emphatically not in the first category. For this reason, Japan's imperialism, while offensive in nature, from the POV of Japan's leaders, was 'defensive.'
(Mind, just because Japan's leaders saw imperialism as a pre-emptive defensive measure doesn't make it so; certainly, Chinese and Koreans for very good reasons would quite strongly disagree with such an assessment. But it is critical to understanding the mindset that drove Japan's foreign policy at the time. 'Defensive,' to Japan's leaders, meant working Japan into a position where she would, through military force, or coercive diplomacy, be able to present dictates to other countries, rather than the other way around.)
For this reason, Japan's gains had to be directly related to preserving her position (often at the expense of other nations, to be sure), even if her ultimate desire was to be as the other ruling Great Powers of the world.
But what this means that even if at some distant point in the future Japan was to seek African colonies, in the short term, it was more important to secure Japan's position in the present. In other words, it was more important to ensure that Korea was a Japanese dependency or colony, or that Japan dominated the Western Pacific, than to get prestige colonies in Africa. As was described then, the "line of advantage" was in Korea and Taiwan, and the Manchuria and the DEI, not in Africa.
This is very unlike the colonial policy of a country such as, say, Germany. Useless does not quite begin to describe Germany's colonial projects; they served no real strategic purpose (Mittelafrika fantasies aside), and were financial sinks, but they served an important role in salving national pride. German leaders probably did have strategic applications in mind for their colonies, but they were not the centerpiece of national or even foreign policy (ie, Germany's efforts to contain Russia were largely entirely separate from her colonial ventures). But for the above reasons, for Japan, imperialism, expansionism, and eventually, militarism, were unified with national and foreign policy from the start, for this reason, it was not worthwhile to spend resources on projects which did not directly relate to the principle goal of foreign policy.
TL; DR Japan has more important things to worry about.