Why doesn't Nintendo make more sequels in the same console generation?

[LemonSlice]

pokeclaudel said

Even if the first Zelda sold 5 million and the second only sold 3 million and the third sold only 2 million that's still 10 million copies sold using the assets.

 

Look at Twilight Princess and then look at Skyward Sword. Do they look like they share any assets?