Because they screwed up the earlier launches unrelated to mining, because they practice annoying market segmentation anyways, because it's seen as a cash grab, because it isn't helping one bit despite the hassle, because stopping mining also degrades the value of the card for resale even if the original buyer is a gamer, and because restricted drivers are DRM and people hate that.

They just have no credibility now so nobody believes it was to help anyone but themselves.