There's no connection with monarchy at all - the only absolute monarchy is Qatar and we know their money comes from a lot of oil per capita. The other countries all have legislatures involving multiparty democracy with or without quirks/flaws (Switzerland has referenda, the microstates still give their constitutional monarch significant executive powers, Singapore's major party has completely dominated since the 1960s). The more obvious thing they have in common is low populations [relative to resources]
I agree that the top of the list is clearly small-population edge cases, but one could also make an argument that strong, consistent economic leadership yields more coordination and reduces waste and thrash in the market (boom/bust cycles, etc).
All of it still comes down to the competency of that leadership though.
