Short answer: because FF7 was a huge hit in Japan, and they've been ripping off Cloud Strife and Sephiroth ever since (the giant sword is now even known as the "buster sword" after its name in FF7.) What, you didn't think the western games market was the only one that made endless shallow copies of its most popular ideas, did you?

As for the spiky hair, same answer as above, except substitute "Dragon Ball" for FF7. Akira Toriyama is almost a national treasure, and his signature style is... spiky haired youths like Goku.

Longer answer: Japanese culture is inescapably tied to the status of the sword, as historically it was a symbol of the authority of the samurai class. It's kind of like the lightsaber, it turns normal everyday peasants into world-saving heroes and unlocks the mysteries of the universe for its wielder, etc. The Japanese are also fascinated by European history and tradition (in the same way that some here are fascinated by ninjas) and they often lift elements for a fusion of both cultures - thus Zelda is a typical Asian "mystic quest" adventure, yet set in a seemingly middle-English world: it's the appeal of the extraordinary. On that note, it's not hard to see the "buster sword" as an over-exaggeration of a heavy English broadsword or claymore, compared to the nimbler, more slender katanas.
Also, Japanese humor tends to be a little more over-the-top than most in the west.
