Not enough jets. Not enough pilots to fly them. Not enough time to train new pilots. Not enough fuel to train the pilots or fly the jets they had.
Germany had the technology and the military know how to conquer and hold Europe if they hadn’t been ruled by a genocidal madman. His destruction of his armies on the Russian front gave the West a chance to defeat him. Of course a leader other than Hitler likely wouldn’t have embroiled the world in a huge war a mere twenty years after the previous one.