Part One:

Post-colonial African nationhood is both fascinating and deeply complicated, and it is something that has been woefully underserved in historical literature generally, particularly English-language commentary. I would make three broad points in response to your question though:

1. The modern political geography of Africa owes a lot to the rapid collapse of European rule on the continent, with retreating colonial powers either being violently repulsed (e.g. in Algeria) or organizing a rapid withdrawal in order to wash their hands of the complications of decolonization. Consequently, there simply was not a lot of time to change the borders of these colonial states even if there was a potential desire from that end.
2. The Organisation of African Unity, one of the leading guiding forces for post-colonial African states, officially adopted a platform of status-quo borders in 1964 in order to promote peace and stability in the young nations of Africa.
3. Despite all of this, there were indeed several attempts to reshape the borders of African nations by both governments and rebel forces across the continent - they were usually just failures.

I'll now go into a bit more detail, but always remember any document that seeks to provide an overview of a continent as rich, diverse, and complicated as Africa is going to be incredibly broad-brushed. For a more fulsome reading into this, it would be best to examine individual case-studies of nations or regions in Africa. I would say more, but I don't want to get into a rant about how Africa is often treated as a monolith.

So, regarding European complicity, it is important to note that European colonial borders were not entirely arbitrary as is often proclaimed. Instead, they were often drawn with specific goals in mind, almost always in the interests of the imperial power, but not necessarily being entirely nefarious or ignorant of local conditions. For example, one of Africa's more peculiar borders, the Caprivi (Itenge) Strip, was carved out to allow for fluvial access between German Southwest and East Africa (nowadays Namibia and Tanzania, among others), which while primarily of benefit to the Germans, would also have been economically and technologically beneficial for their colonial subjects. Caprivi ended up going nowhere because it wasn't navigable, but a large amount of colonial boundaries were drawn up with these concerns in mind. The common refrain of it being done arbitrarily by Europeans with no concern or consideration for the locals or the cohesiveness of the colony is, at best, a huge oversimplification, and it neglects both the variance in colonial structures in African holdings (some of which prised cooperation with the local people as intermediaries and moderately autonomous governors), as well as the much more mundane aspects of European colonialism that drove the majority of decision making on a day to day basis.

Anyway, African independence was a sudden sea-change for most European powers, most of which had intended to, at most, cede independence 20 or 30 years after the 1960s, and oftentimes with no intention of doing it at all. The Belgian Congo, for example, was planned to be given a pseudo-Dominion style status in 1985 (!) by the Belgians, but it was the overwhelming success of Nationalist parties in the 1950s that forced a rapid withdrawal in 1960. Due to the rapidness of the withdrawal, and the chaos that often followed afterwards (cf. the Congo Crisis, the Angolan and Mozambican Civil Wars, and countless military coups) meant that any potential questions of border revision went out the window in the politically fractured post-colonial period.