I also cringe when people toss fabric away - but then, I didn't actually see what was pitched!
I think many people do not realize how expensive it is to ship fabric - I can cram about 9 pounds of fabric into the larger medium flat rate box - but that costs $11.35 to mail if mailed from a post office, $10.85 if the postage was printed on-line.
I think some folks are willing to give unwanted fabric away - if there would not be an additional cost to them to get it gone!