It isn't an arbitrary date, it is called a lunisolar calendar. Btw, the 1.5 billion Chinese use it as well, so the Chinese New Year is always on a different date as well. Would you tell the Chinese that live in the Netherlands that they too aren't good Dutch citizens?
U.S. confirms ISIS computer expert killed in air strike (Reuters)
from the article: Dutch Jews 'vexed’ over queen’s Yom Kippur departure