There are a couple of facts:
-no money, no travel. Even the king said that the family interaction with his counterparts had been very low. Easter with the Greeks and some weddings. Margarita must have had some interaction with the brits when she was at Edinburgh University;
-for the western reigning houses, a princess from the east was not a good political move, as it would have put them at odds with the communist regimes in eastern Europe. What is known from the romanian archives is that the regime was nervous in the '70 because of this possibility. And probably did things about that. We also know that the regime tried his best to prevent Margarita getting hired in one of the United Nation's agencies ;
-maybe the king was strict (or wanted to be), but that was an (over)reaction caused by a very anarchic and dysfunctional family in which he lived even from his birth. He had to deal with his father generation and afterwards with his daughters, who made their own choices in live: 2 out of 5 have mugshots in the US police archives. 4 out of 5 divorced. The girls did not have their private source of income for most of the time. The sons in law bunch includes a former actor with question marks about his relationship with the communist regime, a wife beating guy, the sheriff who made money from cockfighting and a fake french prince "Habsburg" and later on "Laufenburg".