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 for many decades if not centuries.
Also there are plenty of poorer countries with monarchies: Jordan, Saudi Arabia, Morocco, North Korea, Thailand, Cambodia, Bhutan, Lesotho, Oman, Qatar, etc. (I'll admit it's a bit suspect to label North Korea as a monarchy).
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 for many decades if not centuries.
Also there are plenty of poorer countries with monarchies: Jordan, Saudi Arabia, Morocco, North Korea, Thailand, Cambodia, Bhutan, Lesotho, Oman, Qatar, etc. (I'll admit it's a bit suspect to label North Korea as a monarchy).