Different stores and areas have different policies. It will help the fabric get out on the floor if it is large yardage or is already neatly in bags when donated. Those heavy plastic clear zippered bags that sheets and stuff come in are great for small scraps. I can imagine that if a box of assorted scraps comes in it does often get sent to the fabric recycle.
One of the Goodwills near me always has lots of fabric. Small pieces that no other store would sell separately are priced separately, they bag lots of stuff in to comic book sized bags as well. One of the other locations seemed to have a sudden shortage of fabric a few years ago, was talking to the clerks and they have a donation quilter that they just give the bags of scraps to, they don't even get out on the floor. Bummer for me, but good for the scraps getting used. At the Goodwill near my mom's house all the fabric is either bulk yardage or in the comic book sized bags. All I can say is the person who puts those packages knows what they are doing to make them appeal to a broad range of people! Nothing like sticking a non-quilting suitable piece of something to get people to buy them like putting it in with quilting suitable material.