(8) The curse of the British class system, which burdens society with too many parasites towards the top and disincentivizes the bottom. Britons never reconstructed anything with this system, because it arose at the apex of an empire in which Britons were the beneficiaries of the surplus labor of non-Britons.
(9) The US has all the levers (and more) to ensure the UK is never functional or independent, and uses them continuously.