As well as the crucial point lostlogin raises, the Allies were assuming the Abwehr were rather better at espionage and reconnaissance than they turned out to be. Some was discovered via SIGINT from Bletchley and some not until the fall of Berlin.

Just as well as one of the British officers (Strangeways) was making the southern deception rather difficult by disagreeing with everything.

The Allies had to assume the Germans had a working spy network in the UK, turns out they had none and we caught or turned the lot. Those agents (including Pujol), the extensive continental networks and Ultra meant they could spread disinformation effectively and check to see if the bait was taken, repeatedly.

It could have been a lot more difficult if Hitler had listened to his High Command a little more.