My personal guess that it's the combination of at least the three points you mentioned. Discovery via grapevine, combined with the ability to move the purchase

My personal guess that it's the combination of at least the three points you mentioned. Discovery via grapevine, combined with the ability to move the purchase between devices - regardless of vendor. It is possible that a "once burnt, twice shy" effect is amplified by the 3/11 rule. It takes one bad experience with DRM'd goods for a person to realise that something is wrong, and once they learn that DRM was the reason for their problem they will broadcast their discovery about the anti end-user experience. And as any news reporter knows, bad news travel fast.