Hamburg was well-defended but it wasn't the industrial heartland of Germany, it was an historical city with a correspondingly large number of wooden buildings.
I think you're getting mixed up with Lubeck. Hamburg was the largest industrial city in Germany. The buildings were mainly brick or stone.
From The Battle of Hamburg by Middlebrook:
It is often believed that the raids of the Battle of Hamburg contained a specially high proportion of incendiary bombs but this is not true. It is also believed that Hamburg was a good fire target. This also is a misconception. Because of Hamburg's great fire of 1842, the city contained few really old timbered buildings; most were of fairly modern brick or concrete construction. There was also the presence in Hamburg of so many waterways which might act as firebreaks and which provided convenient sources of water for the city's fire-fighters. Hamburg would not be an easy city to set alight and a study of Bomber Command records shows that the bomb-loads of the first raid of the Battle of Hamburg contained a lower proportion of incendiary bombs than other city raids of this period. The increased number of high explosives were needed to blow apart the strongly built buildings of the city.