That only applies to Taipei itself. That's where the concentration of historically middle class KMT supporters that fled the mainland are the highest. It's also one of the roots of anti-mainlander sentiment in Taiwan itself, with many Taiwanese seeing themselves as a higher class than the historically poor Chinese peasant. There is a connection here to the cultural revolution too, but that's too complicated for this post.

On the national palace itself - it's a topic of some contention because it reinforces the PRC's claims on Taiwan. It's not uncommon sentiment for Chinese netizens to demand the return of Chinese artifacts and gold in the event of Taiwanese independence. After all, a non Chinese country should not be holding onto significant Chinese artifacts.