Because AMD stopped making the 72-73 and 73-76 quarters. Reason being they were selling them as 72-76 quarters thinking they were all the same(they aren't) They had the mold screwed up(too short). So what ones are out there still are from independent sellers and they know there is no timeline as to when AMD will refire that mold up again.
Save yourself some money, Amazon sells Goodmark quarters, with free shipping. I have one of both and I'd rather have the Goodmark over the AMD