Because starting with the desired result first and then going backwards to justify that result is completely unscientific and any exploration made on this premise is flawed.
Who said anything about this being a scientific exploration?? Black Panther is a superhero comic book... It's exploring the themes around non-colonized Africa and an African king/superhero narrative as speculative fiction.
And I doubt that anyone at Marvel has enough experience as a historian to even begin to make an informed exploration of alternate history.
Wait... now you need to be an experienced historian to write speculative fiction about a subject??
Especially as the comics are still intended as light entertainment with mass market appeal so they go with the rule of cool and whatever their marketing department things the target demographic likes instead of doing actual historic evaluations.
Light entertainment with mass market appeal describes some comic books... not all but some. Not sure how much mass market appeal an African king/superhero of a technologically advanced culture that was never colonized had in the 60's... *shrug*
Archaic as in their head of state is chosen by single combat.
That would be cultural tradition... no more or less archaic than being the ruler because you happen to be born lucky... right?