Likely because it is un-registered , and would need the rear lights sorting and any other bits associated with the process.Unless the mileage is colossal ,or other faults, it may be about right. If it checks out, and the ad suggests carfax and hpi are clear, it could be a good buy. Think this advertiser is importing s197 Mustangs in quantity , most of these are on salvage titles ,but priced to sell.
Any 'respectible' seller will give you the vin no. - run it through Google - you can often see with a little investigation whether the car has been on the USA 'hit list'. Unscrupulous sellers will often register the cars in UK stating that the car is HPI 'clear' but not mention it was US salvage.
Advert now "gone." Need to know what you are doing to buy that car. No mileage quoted, or what spec/extras it has, but does have the navigation screen/HUD switches, so could be high spec. Fact it has the headlight washers indicates it is a UAE/Dubai spec car, so maybe registered new there? Understand these are a mix of US and UK, Euro spec cars e.g. has the headlight washers but US lights (certainly at the rear /no side repeater light). Not sure how you find out if a Dubai/UAE car has been written off, or heavily accident damaged & repaired previously?