Answer: because Maggie does not appreciate their artistic value.
In "Everyday Use," Dee believes that Maggie does not deserve to have the quilts that their grandmother made. Dee believes that the quilts are an artistic piece, and that they should not be devalued by using them everyday in the way Maggie would like to. Maggie would indeed like to use them for what they were designed, which is as quilts. This shows the very different personalities of the two sisters.
