C) Surely some of those cars are worth more than the £2k the previous owners scrapped them for?
Probably, yes. I'd imagine most of those Golfs are worth, privately, £2-3k. But if they are worth £1990 trade, for example, then a dealer will simply put the deal through as scrappage instead. A car with a trade price less than the scrappage threshold might be worth up to £3500 on the retail/private sale market. But franchised dealers wont put cars like that on the forecourt so would never get retail money for them.
Instead, they are destroyed.