I think it was Germans not trusting themselves. They could of brought them, their allies wanted them to buy them (take some pressure of the RAF and USAF if the cold war kicked off) and they had the money. But they didn't.
Random relavent(ish) point: The Abrams, main tank of the US army, has British armour and a German gun. It does have a US engine, that's why fuel economy is so poor
