Here are my two cents:
It is an unfinished car. Unfinished projects are always harder to sell than proven turn key cars. There are a lot of loose ends to be tied according to the ad. For example a good chunk of money still has to be spent on this vehicle to get the suspension and brakes up to the level of the engine performance. Since there is a bunch of stuff left to do and some of the work is described as medium quality, the PP board bargain hunters are out.
I also am wondering if the RSR builds have become a bit less fashionable these days? I would still love to own one. Personally though, I would not settle for anything without a 3.6.
George