Writing Systems of the World 4, Exercise 1: syllabary fit

From Chapter 1: a syllabary symbol stands for a syllable or mora. So the
number of symbols needed equals the number of distinct syllables the language
allows.

Japanese uses mainly CV syllables (the Syllabary article), so the list of
possible syllables is short and the syllabary is small and regular.

English allows complex syllables with consonant clusters at the start and
end. The article says English would need over 10,000 separate glyphs as a pure
syllabary, which is why alphabets handle such languages better: a few dozen
letters combine to spell any syllable.