You can learn Japanese for many reasons. An ancient culture, a thriving economy, interesting people, and splendid landscapes are some of the things the Land of the Rising Sun boasts of. You'll be hard pressed to pick your main reason, though this partial list will strive to persuade you; and if it doesn't, then perhaps a hop to Japan will convince you. But first, the list.
Akira Kurosawa - Director Extraordinaire
You have missed the art of extraordinary director Akira Kurosawa if you have not seen Throne of Blood, Seven Samurai, Dreams, and Ran. With his attention to detail, beautiful landscapes, gripping stories, and climactic scenes, these movies are a must-see for the serious movie buff. Because these are all created in the director's native language, you have to learn to speak Japanese in order to experience these movies' timeless appeal.
Japanese Anime
Obviously, Japanese anime isn't for everyone. When you are used to animations by Pixar and Disney, anime's attributes like the onomatopoeic typography, speech bubbles, and over-the-top physical attributes can be strange. However, it does have engaging storylines and fantastical creatures. You will have a good reason to study Japanese with Naruto and Dragon Ball Z.
Chindogu, A Japanese Art
Japan boasts of various art forms such as the tea ceremony, ikebana, and origami, but none is as interesting as chindogu. This art form is all about inventing inconvenient gadgets for regular use, but with the most noble intentions. In fact, these inventions only ever bring on the laughs as an achievement.
Maybe you're interested in a tissue dispenser atop your head as a hay fever hat? Or perhaps a noodle-eater hairguard to keep away hair from your bowl of ramen? You might be able to transform these chindogu items into profitable items if you speak to the inventor; thus, why you must study Japanese. Strange things like these actually occur.
Japanese Food
From sushi to wasabi, Japanese food is a delight to the senses. It might seem very easy and very pure on the surface, but the creation and presentation involve much effort and a perfectionist's attention to detail. To speed up the process of learning how to cook like the Japanese, you should study Japanese! After all, you want to learn Japanese cooking, not annoy your chef-mentor with running questions on what anko and umeshu are.
Japanese Fashion
Japan's outlandish street fashion can't be topped, even by New York. You will enjoy the avant garde costumes donned by Tokyo's young people like Ganguros, Lolitas, Bosozoku, and Kogals.
If you still need reasons why you must study Japanese, consider that Japan is the fastest rising economy in the world and they're the third largest Internet users. These should wake you up to the business opportunities Japan has to offer!