>>17758528 (OP)Because it ceased to exist after WW2. The USSR saw the fall of White regimes in Africa as advantageous because the Black rebel groups often were amenable to, and often explicitly supportive of Third Worldist Marxism and therefore friendly with the USSR. The US saw the fall of White regimes in Africa as advantageous because it weakened Western Europe and them more reliant on the US, and because it opened up African markets to American companies. In some instances with the US there was an ideological motivation as well, ranging from crypto-Marxist in the FDR government to earnest believers in race-blind liberalism under Reagan who all had ideological reasons for opposing White supremacist governance in Africa.
I'm not sure I would lump the UK and France in here. France fought an incredibly bloody war to maintain its control of Algeria, and early on in the Cold War the UK was interested in trying to hold the Empire together. Eventually both caved to African independence and attempted to maintain some semblance of control via soft power organizations like the Commonwealth and La Francophonie, to vary degrees of success. Of the four, France tried to maintain normal relations with South Africa the longest but was not strong enough alone to weather the shifting social climate.