Paper lets the flour breathe, releasing moisture. The grain isn’t 100% when milled and the milling process generates significant heat (mill some grain at home with a motorized mill and see). Warmth + moisture + hermetically sealed plastic smells like a nice way to grow some fungus.
Edit: isn’t 100% dry when milled.
It’s for a 3/4 cup serving which doesn’t seem all that unreasonable.