So your argument is that only someone exactly as insane as OTL Bokassa would ever create or retain a monarchy in the CAR?
I wouldn't go quite that far, but OTOH, the default since the early 1920s is for new nations to become republics. Other than Malaysia, which is an edge case because it incorporates several traditional monarchies, I can't think of a country other than the CAE that has become a monarchy since then without having a pre-existing dynasty. So, while it's not impossible for an African country without a traditional dynasty to become a kingdom or empire, it wouldn't be
normal by 20th-century standards, which means that sort of thing would appeal mainly to those of a... grandiose turn of mind.
There are other possibilities.
Brian Titley has argued that there was method to Bokassa's madness, and that his coronation as emperor was an attempt to unite the country and legitimize his rule by making him the Big Man over other local Big Men. If so, though, he was doing it wrong. For one thing, holding a coronation that costs more than the country's GDP isn't a way to win friends and influence people, and for another, there was little if anything about his monarchy that was African. The coronation ceremony and regalia were Napoleonic rather than drawing from indigenous tradition, and the
coronation ode celebrated Bokassa as "the most illustrious of the French" rather than the most illustrious of the Central Africans. France was the abusive father whose approval Bokassa wanted, and from all appearances, his decision to become a monarch was more about that than about nation-building.
But maybe we could imagine a different ruler of the CAR, one who doesn't have Bokassa's grandiosity and capriciousness. This ruler - let's call him Kobassa [1] - takes a look at his patchwork country and really does decide that monarchy might be an effective unifying symbol as well as a clean break from French political tradition. He makes sure to get buy-in from the local elites first, has a lower-key coronation, and combines the customs and regalia of various pre-colonial kingdoms in the region (as well as the pre-state peoples) when he establishes his court. If Kobassa is an effective and even-handed ruler, then maybe his kingdom might last. But that's a very big "if," and any newly-established monarchy in 1970s Africa would be fighting against political gravity.
[1] His name certainly wouldn't be Barthélemy Boganda, given Boganda's attachment to French republicanism.