I was involved in this before Unicode be a e Unicode when it started as discussions with Xerox and Apple—Xerox at that time had their XCCS standard. Those discussions directly morphed into Unicode. [[I was even there when we picked the name Unicode for what we had home to produce.]]

Conceptually we long debated unifying everything and in an ideal perfect world we would have done it. The reason was one primary goal for a new standard was to make it easily parseable and having unique rather than repeated codes was key to that. Sadly in the end we did not unify everything only to get buy-in from all major countries to support. That’s even why you see the roman/asciii characters repeated within Unicode itself—like as romaji. This was all well in good until we came to CJK and the number characters with semantical overlap was huge that this was more seriously considered—infact we started investigating this at Xerox before even thinking about Unicode and that work predated and influenced and leveraged the work done later.