In short, seventeen syllables in Japanese equal fewer words than seventeen syllables in English. A count of seventeen syllables in common English represents quite a few words. For this reason, adopting the traditional Japanese syllable count can have a detrimental effect on an English haiku. An inexperienced haiku poet will feel obliged to fill the space. They may add unnecessary verbal phrases, where an object could simply be placed in the poem without comment. For example, to take the equivalent of hototogisu, a poet might write such a strained line as 'Hearken the cuckoo!' to obtain the 'correct' syllable count, not believing that the more direct and dramatic 'Cuckoo!' could stand by itself in disyllabic glory. Alternatively, the poet might pad their line with decorative adjectives to achieve the count. The resulting haiku will have lost an essential quality of simplicity - all for the sake of a misapplied 'rule'.
A better guideline than counting syllables is to approximate the word count of a Japanese haiku. Translations are good models for this. Read some Japanese haiku in translation, preferably with a parallel Japanese text, and compare the arrangement of words and syllables in the two versions. Most poems in translation will be shorter than the original Japanese.
Gates monopoly
He found no single action
Beneath his dignity