ASCII being 7 bits made it easy to support a larger 8-bit character set that extended it on 8-bit systems, but that is not why ASCII is 7-bit and not 8-bit.
If ASCII where 8 bits to start with, we probably would have had zillions of incompatible extensions that used Control-N and Control-O (shift out and shift in) to switch into and out of 'non-ASCII' mode (here's an idea to sort-of improve upon HTML and XML: instead of < and >, use shift in and shift out to delineate nodes. That way, we wouldn't need that < stuff)
Alternatively, the nine bit byte might have won the battle.
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ASCII being 7 bits made it easy to support a larger 8-bit character set that extended it on 8-bit systems, but that is not why ASCII is 7-bit and not 8-bit.
If ASCII where 8 bits to start with, we probably would have had zillions of incompatible extensions that used Control-N and Control-O (shift out and shift in) to switch into and out of 'non-ASCII' mode (here's an idea to sort-of improve upon HTML and XML: instead of < and >, use shift in and shift out to delineate nodes. That way, we wouldn't need that < stuff)
Alternatively, the nine bit byte might have won the battle.