Here's why:
* Syllabication rules: Syllables in English are generally formed around vowels. The vowel sound in "human" is the "u." Therefore, the syllable break is after the "u" and before the "m."
* Pronunciation: When we say "human," the stress falls on the first syllable "hu" and not on the second syllable "man."
So, the correct syllable division is hu-man.