Originally, it probably was a syllabary—a script where syllables are represented with characters—with symbols that were not needed being removed.
ɚɹˈɪdʒɪnəli, ɪt pɹˈɑːbəbli wʌzɐ sˈɪlɐbˌɛɹi—ɐ skɹˈɪpt wˌɛɹ sˈɪləbəlz ɑːɹ ɹˌɛpɹᵻzˈɛntᵻd wɪð kˈæɹɪktɚz—wɪð sˈɪmbəlz ðæt wɜː nˌɑːt nˈiːdᵻd bˌiːɪŋ ɹᵻmˈuːvd.