I guess the easiest way to explain would be to try to figure out the difference in perspective we're dealing with. So I'm asking (quite honestly, not a rhetorical question, not sarcastic): why do you think they shouldn't? Their kanji carry a lot of meaning and nuance, and they learn them naturally (though to varying degrees). Without them, not only would their language lose some expressiveness, but it would be a nightmare to figure out, as you see in @ギョルギ九十三's example - just think of how many kanji are read the same way.
So, to get an answer, we should maybe ask ourselves the opposite question: why would they need to change it?
Using @ギョルギ九十三's example, if you focused only on spelling and were reading hiragana or romaji text, you would find that there's 3 "hashi" words used. Even if you put in a space between words and particles, you couldn't tell the difference between these words without context. Using katakana instead for vocabulary and preserving hiragana for stuff like particles might make it clearer, but you still suffer from the loss of meaning, and therefore context.
This is a problem, since Japanese tends to be fond of dropping context in the middle of things, which leaves you quite a bit lost. It's part of what makes Japanese a bit intimidating.
That's why kanji exists as it serves to deliver the message more accurately. If you considered that meaning carries more weight than focusing on spelling, the message is still conveyed. Spelling matters when you're the messenger as if you were speaking, but its meaning still has to be properly understood on both sides. Unlike Western languages, when you don't keep to one script, it's a lot more simpler than having to spell everything out.
All this is where I'd say that Japanese is not the difficult language that it's cracked up to be, unlike what everyone else might say. The only difficulty is not knowing much about it, and some of the overwhelming uses in the language. Once you sort that out, it actually is quite simple.
All this is where I'd say that Japanese is not the difficult language that it's cracked up to be, unlike what everyone else might say. The only difficulty is not knowing much about it, and some of the overwhelming uses in the language. Once you sort that out, it actually is quite simple.
This! Thank you, @icepick87, I keep trying to explain this to people who ask "but isn't it very hard?" Japanese, like any human language, has evolved to be as it is because it makes sense to its speakers. The way it makes sense may be different, but trusting that it makes sense is an important part of learning it, I believe. In time, we can pick up on the patterns, our brains are very good at that. Similarities are where you look for them, as are differences.
I keep trying to explain this to people who ask "but isn't it very hard?" Japanese, like any human language, has evolved to be as it is because it makes sense to its speakers. The way it makes sense may be different, but trusting that it makes sense is an important part of learning it, I believe. In time, we can pick up on the patterns, our brains are very good at that. Similarities are where you look for them, as are differences.