The ruins of the citadel and fortress means something. They provided protection against invading forces, and in its time, people needed that protection and care. The cities of Transylvania were often built around fortresses like these. Many have been either abandoned or restored. They provide a vital draw for the tourism industry either way.
The same holds true for other castles that were built to protect the people and livestock. Keep in mind, the Kings needed armies and these armies needed men. If men, women and children were killed, then the Kings would have to patiently re-populate their land with fewer people and it would take more time.
This is why the Alba Iulia citadel ruins seem to hold more of a past than others. It is an important part of Transylvania and its history.