Could be that the Rogue Sphinx debuted in 2014 and then the V2 was introduced in 2016. Followed by the V3 in 2020.
Hence, there are those that will wait for (how much longer?) for the V4 to come out. I mean, the law of averages is that there should be a new version this year.
Rogue brought out the V2 of the RP-5 not long ago and- just before and just after- I saw a spike of RP-5's on sale on the usual sites. Fair drop in price after the new version appeared.
Each audio mfg differs and when you consider how few times a company like Rega comes out with a new product vs. a company like Rogue - which has a fair amount of offerings out there and in the pipe - it would make sense that a Rogue product that is "due" for a upgrade is also found readily available on the used market.
It is also likely that the market of many sub-$1000 integrated's is inundated with popular well-known brands (Denon, Marantz, Sony, Yamaha, etc) and while we all know about Rogue on this site, the vast majority of the public is not as acquainted with them. Perhaps if Rogue was sold in Best Buy, or via Crutchfield, they would have much more name recognition. Although the Sphinx is was never a sub-$1000 integrated offering. Plus there is no HT Bypass - like the RP-1 - nor a processor loop. Perhaps if they made it more home theater usable instead of offering it with good phono and headphone inputs they could gain market share for a wider audience.
@OP
Curious, for those that have one on the market...why are you selling it?