The answer becomes apparent the more you study Japanese.
Japanese is full of homonym . There would be no way of distinguishing them, unless the context was really obvious, if you didn't use kanji.
Attempts were made in the past to simplify Japanese into kana or even just romaji, but they failed. It just wouldn't work.
In English, we can distinguish words that sound the same by spelling .... pair, pear, pare, etc.
In Japanese one kana = one sound. There are extremely few exceptions, like how は sometimes sounds like "ha", but sometimes "wa".
Just try writing an entire letter in kana, and see how difficult it will be for someone ( even to the Japanese ) to read