because you tend to find owners clubs over value their cars compared to what the rest of the world value them at.
with petrol getting ever more expensive by the month you'd be suprised at how fast the value of a big engine car starts to drop. people who can't afford to run them want rid quick so sell low, and those looking to buy want a bargain because they are buying a big engine in expensive times. Dealerships offer low PX on them as they know they'll struggle to shift a big engine compared to an eco car.
Value wise, a UK car with this spec is not £6.5k though. Had a quick scan on AutoTrader and they are minimum £8k mark for private sale. Although this isn't the actual sale price, I am sure they aren't selling some 25%-30% lower than that.
As for 'club owners' - I am actually finding a lot of the valuations on here under what is being offered on PH, AT and the like. If this is based on people monitoring many actual sales over many months then fair enough, but it seems the opposite is happening, that on here the valuation is too harsh