Used graphics card were/are a big market (even though new cards depeciate massively when used). Usually crypto cards still last a decent amount of time (and might even have been thrashed while water cooled to keep them healthy). The price of them make up for the fact they have been ran constantly. And the price makes up for the fact of being outdated in-terms of performance. They are great for budget PC's. Many people still buy GTX 970's etc.