Here's why:
* Haiku's unique structure: Haiku's 5-7-5 syllable structure is unique to Japanese poetry. While Chinese poetry has different forms and syllable counts, it doesn't have the specific structure of haiku.
* Origins in Japanese poetry: Haiku evolved from a Japanese poetic form called hokku, which was part of longer poems called renga.
* Focus on nature and brevity: While both Japanese and Chinese poetry often deal with nature, haiku's unique focus on capturing a fleeting moment of nature in a concise way is distinctly Japanese.
While Chinese poetry certainly influenced Japanese literature, haiku is a distinctly Japanese creation that developed organically within its own cultural context.