Well, the purpose of the magazine is not only to educate and stimulate the readership, but to also support their advertisers by encouraging the purchase of products. They also know that different skill levels of quilters will make these quilts, that the cutting skills are not the same, so they've allowed for lots of extra so the quilter will have enough to repeat if they make a mistake.
And then, too, the magazines and the pattern makers know that the prints they feature will be off the shelf quickly, to be replaced by the next season's collection. So the quilters often can't get more. The consensus is, better more than enough than not enough/better to err on the side of extra!
Jan in VA