Because Japanese has three writing systems. Hiragana are their “alphabet”, and give you a phonetic reading of each word. Katakana are variants of hiragana, and usually used only for emphasis, loan words and certain names. Then they also have kanji, which are characters borrowed from Chinese. Because Japanese has a lot of homophones (words with different meaning that sound the same), they use kanji for a lot of writing.
The list I wrote above only has the words written out in hiragana. I have now also given the way you can write them in kanji. If you want to become fluent in reading Japanese, you’ll have to learn about 2000 of these kanji to read an average book, but that’s not something to worry about too much in the beginning.