Couple of reasons.

1) A new smaller, somewhat improved version has recently come out.

2) While its a fun module, there were some issues such as unstable internal clock, general confusion as to how the knobs worked/related to one another.

So, between the draw of something new and shiny coupled with some dissatisfaction has made a lot of people sell it. I've seen them go as low as $150 recently.

Personally, I sold mine because I found a random module that better fit my needs with the SSF URA.