Agree with Stoner but also I don’t think you’re hitting that bigger marketplace on STW; we all might think STW is the centre of the MTB universe but its not, so to find a buyer after a specific frame is actually quite rare IMHO…and even if you do it might not be in in the right size, colour, condition etc.
So if the frame isn’t exactly what a buyer is after then they are not normally prepared to pay top whack. The price gets dropped, and dropped until eventually its cheap enough that even if it ain’t perfect, its good enough and, if its not good enough, they can flog on eBay for what they paid or more!