Thanks for the more information! I may not have known what I thought I knew. However, some googling leaves me still unsure.
This web page suggests that the earliest known written languages were all vowel-less, including the ancient Egyptian alphabet, Proto-Canaanite, Phoenician, and South Arabian. It doesn't mention Akkadian though.
Other googling suggests Phoenician developed from Proto-Canaanite. Even if other written languages with vowels were around at the time it developed, I don't know if that means it was a _purposeful choice_ exactly. Just based on how languages works, it seems plausible it just evolved from Proto-Canaanite by people who knew how to write Proto-Canaanite, which doesn't necessarily mean they thought "Gee, should we add in vowels like those Akkadians?" I don't know if we have any way of knowing?
But you may know more about it than me, or what I found on google.
That page does mention Akkadian in passing, by referring to "Cuneiform". It accurately notes that there are many more cuneiform signs than there are sounds being represented, and so it's not really right to call cuneiform an "alphabet". However, it is still true that (particularly by that point) cuneiform writing obligatorily indicated vowels.
A fun fact that I particularly like: the form "Ra" for the old Egyptian sun deity is a transcription convention which transcribes an Egyptian consonant as the vowel "a". The Egyptians generally did not include a vowel in their writings of the name. However, we actually do know the vowel used in the god's name, because he is mentioned in diplomatic correspondence, written in Akkadian. The vowel is [i] (as in the English word "bee"), occurring between the R and the "A" (which is actually one of those back-of-throat consonants that modern Egyptians are so proud of).
This web page suggests that the earliest known written languages were all vowel-less, including the ancient Egyptian alphabet, Proto-Canaanite, Phoenician, and South Arabian. It doesn't mention Akkadian though.
https://www.ancient.eu/alphabet/
Other googling suggests Phoenician developed from Proto-Canaanite. Even if other written languages with vowels were around at the time it developed, I don't know if that means it was a _purposeful choice_ exactly. Just based on how languages works, it seems plausible it just evolved from Proto-Canaanite by people who knew how to write Proto-Canaanite, which doesn't necessarily mean they thought "Gee, should we add in vowels like those Akkadians?" I don't know if we have any way of knowing?
But you may know more about it than me, or what I found on google.