One reason the kanji in Japanese are so complex is the way the Chinese words and characters were borrowed into the language. English has multiple “readings” for the same “kanji/concepts” as well. We have “ward” as well as “guardian” because both were borrowed from different French dialects at different times.
There are many examples of words we borrowed from languages descended from Latin like French and Spanish, that we later went back and “re-borrowed” from Latin itself. The situation is comparable in Japanese, where some readings/characters were borrowed from older versions of Chinese, and then later re-borrowed from more modern Chinese languages.