The Sinmungo (Drum of Grievances) that appears incessantly in Chinese historical dramas

The Sinmungo is a political symbol intended to convey the voices of the lowly and the wronged to the highest ruler.
It is said that it briefly existed in China during the Song Dynasty.
Therefore, the Chinese Sinmungo appears frequently even though it was never actually rung.
In Joseon, King Taejong established the Deungmun-go in 1401.
This was the origin of the Sinmungo during the Joseon Dynasty.
When watching Chinese historical dramas, you see nobles wearing Joseon gat (traditional hats)
and dressed in Joseon-style clothing.
Why do they do this, even though they never wore Joseon hats or clothes back then?
During Mao Zedong's Cultural Revolution, they threw away and burned everything they deemed good;
why are they suddenly claiming our things as their own?