Why are there so many Chinese characters in Japanese calligraphy?

In the past, Japan, South Korea, North Korea and Nanyang were all dependent countries of China, and the official language was Chinese. People with status, such as royalty and nobles, all use Chinese, and they are proud of knowing Chinese. The books, poems and paintings left behind are also China's. So of course they write poems in Chinese. As for why Chinese characters are still used now, one of the reasons is habit. The second possibility is that they have few words, many of which have the same pronunciation, so sometimes there will be ambiguity without Chinese characters. Third, they may not feel that they are using China's Chinese characters, and their Chinese characters have been integrated into their culture.