It's hard to explain. In English, spelling, pronunciation, and meaning are all more or less interrelated, right? In Japanese, writing (kanji) correlates to pronunciation and to meaning, but pronunciation and meaning are mostly unrelated to each other. Kanji is what disambiguates them.
So, obviously learning 1000 kanji isn't easy. But doing that is what makes it possible to learn 100,000+ words whose pronunciations and meanings would be otherwise largely unrelated.
It's quite similar to the role that Latin/Greek roots play in English. When you see a word that includes "-graph-" you know it probably involves writing, and similarly when a student of Japanese sees a word with "間 (kan)" they know it involves an interval or space. Throw away the kanji, and your student now just sees "kan" - which means the word will probably involve an interval -- or a barrier, or emotion, or appearance, or a tube, or a building, a warship, a crown, an ending, China, a publication, a government ministry, or.. you get the idea.
A lot of people think that and personally as someone fluent in Japanese (as a second, well rather something like fourth, language) I also sort of feel the same way. However if you look at it without the learned biases, there is a great example where a country with fairly similar language in terms of grammar and sounds that had used to use chinese characters switched to a phonetic alphabet and are not noticeably worse off for it: Korea.
So, obviously learning 1000 kanji isn't easy. But doing that is what makes it possible to learn 100,000+ words whose pronunciations and meanings would be otherwise largely unrelated.
It's quite similar to the role that Latin/Greek roots play in English. When you see a word that includes "-graph-" you know it probably involves writing, and similarly when a student of Japanese sees a word with "間 (kan)" they know it involves an interval or space. Throw away the kanji, and your student now just sees "kan" - which means the word will probably involve an interval -- or a barrier, or emotion, or appearance, or a tube, or a building, a warship, a crown, an ending, China, a publication, a government ministry, or.. you get the idea.