Why is the pattern anchored to the art board and not the item? I often create shapes and apply a pattern (lets say a plaid) and I adjust the alignment of the pattern so that it is equal on all sides. If I then copy the shape containing the pattern so that I can then offer the client a different color combination of the pattern, I now have to nudge the pattern of the new shape to align properly again! Because the pattern is anchored to the art board not the shape.
This behavior can be toggled in Preferences > General > Transform Pattern Tiles.
Once enabled, the pattern stays relative to the object it’s applied to, when you move or copy it between documents.
It also makes it deform if you stretch, resize, rotate, skew or transform the object, because it’s all a part of 'transformations' we can make.