Earlier quoted context omitted.
I would point out that Sweden is unique on that list, as although they do have a monarchy, the king hold no legal/political power, not even in a "symbolic" sense. A potential explanation for the phenomena you've observed is that it's uncommon for new monarchies to be started in the 21st century, so the countries that still have monarchies are all countries that for the most part have had stable forms of government fo…
Did you just list Saudi Arabia and Qatar as poor countries? They might be anything, but not poor.
Qatar is absurdly rich, but the wealth is inequitably distributed (unusually so). Although the GDP per capita is ~60k, the median household income (and the median per-capita income) are considerably lower than the countries the parent comment mentioned.