I am familiar with the [history of why these two writing systems were invented](https://japanese.stackexchange.com/questions/4281/why-was-both-katakana-and-hiragana-created), and my question comes more from a modern practical standpoint.

In my understanding, hiragana and katakana both have same sounds, they are just written differently. Katakana is for foreign words and onomatopoeia, and hiragana for everything else.

So I'm just curious why weren't these two systems merged into one to make it easier to learn to write in Japanese?