It was the trend to demonstrate power and resources by building large temples. The rulers often invested a lot in the decoration and maintenance of the temples. So the foreign conquerors made them target first. The most prominent example of it was the temple 6f Somnath in Gujarat looted several times by Sultan Mahmud of Ghazani who came from Afghanistan. Much of the wealth he carried away was used to create a splendid capital city at Ghazani.