Why do Japanese have Chinese characters?

Because early Japan didn't have its own characters, it could only be used with the help of Chinese characters in the more developed Central Plains.

Later, I found it difficult to integrate Chinese characters with Japanese, so I simply created Hiragana and Katakana with Chinese characters, which is today's Japanese.

Many people actually have a misunderstanding that written language is relative. However, in fact, the number of languages in the world is dozens of times that of written languages. Most languages don't have their own characters, so they can only be marked and written by other characters.