Others like Biertan are now UNESCO protected castles, and are tourist attractions. The Romanian government promotes these castles as tourist draws, and unlike the city of Alba Iluia, where there is a strong culture of past Roman Empire, and as the capital city of the Principality of Transylvania, Biertan was a Saxon village.
Others, like Bran Castle are famous by the people who lived-- or didn't live there. Queen Marie of Romania lived there, but not a Count Dracula. Count Dracula was made famous by Bram Stoker, as was this castle-- Bran Castle in Transylvania.
As for others, they are ruins in a national park, and are left to fall into disrepair. In this case, it is just as well since Elizabeth Bathory lived in these walls-- and she was a notorious serial killer. After her death the castle remained until it was looted and burned. After this, it became a part of the series of national parks, where endangered plants are known to be found.
These castles are of course a vital part to the history of Transylvania.