That would work nicely in an abstract spherical Japan in pure vacuum.

The hardest bit about redoing something from scratch is not how to design the new system, but it's in getting it adopted. Many societies have tried things like that, social inertia, especially paired with learning barriers (the steeper, the worse), and cultural and political notions (and Japan values and tries to preserve their history and culture quite a lot) is not something that can be just dismissed.

That's not to say that there weren't countries that had writing system overhauls, just that it's difficult and of questionable value and not entirely without negative effects.

Most of the confusion in written Japanese stems from the use of kanji. The Kanamoji Kai (カナモジカイ) was established more than 100 years ago by Yamashita Yoshitarō (山下芳太郎), and it has been advocating for the abolition of kanji for many years, though without much success.

https://www.kanamozi.org/

If you watch a Let's Play of マザー２ (the original release of the cult classic SNES game EarthBound), you'll notice that writing Japanese using kana alone is not only possible, but that most native speakers have no trouble reading it -- although some claim that having a few kanji makes it easier because of homonyms.

https://www.youtube.com/live/F_UrqsO2JQ0?si=-1r-FbCZCJ3rt-Z1...

You are getting downvoted, but I have heard Japan has surprisingly low literacy rates (well below the 99% stated by the government) for just this reason.