I'm still learning Japanese so apologies if this isn't 100% accurate. Unlike English, Japanese is typed phonetically but there are different words with the same pronunciation. For example, ???, ???, and ??? (and probably some others that I haven't learned yet) are all pronounced and typed as "katte". Likewise, ?, ? and ? are all "ki". The UI that appears is for selecting the word that you want.
As for why Apple doesn't have something similar for English, I wouldn't have a clue