It's nothing more than the natural ebb and flow of sales and purchases here at Head-Fi. In the several years that I have been a Head-Fi member, I have seen it happen time and time again with just about every one of the popular headphone brands/models. Last month it was the D2000s/D5000s, this month it's the GS-1k, next month it will be some other model of headphone. Happens all the time. As for each individuals motive for selling, it's hard to say - could need to raise money to pay bills, don't like the headphones, wanting to upgrade to something else so need to raise funds, etc, etc...