why are these not 5-7-5?
Japanese poetry is structured by on (lit. "sounds"), not syllables as understood in English. Because the typical on, being either a vowel, a consonant + vowel, or the "n" sound, is shorter than the typical English syllable a 5-7-5 English syllable poem ends up being significantly longer than a Japanese one. It is my feeling that 4-6-4 (or even shorter) better matches the brevity of Japanese haiku.