It's really a lucky happenstance that Semitic languages have enough gutterals that could be repurposed as vowels; if these had been lacking, or if Greek had needed them as consonants, then it's easy to imagine a sort of incomplete consonant-only orthography coming into use, perhaps even persisting to Latin alphabets in the modern day. Greece's first introduction to writing (linear b) didn't stick and doesn't seem to have been used for anything other than palace records, arguably because of deficiencies in that script, might literacy in the West have similarly been stunted by scripts that could not show vowels?
Losing the vowels works in languages like Arabic because of the structure of the language, with consonantal clusters (e.g. ktb, tlb) being semantic “roots”. So you usually know from context, and if you don’t know the absolutely precise word, you know the meaning, which can sometimes be more informative.
