In Singapore's case, I'd say it's because of a strong commitment to free markets, zero capital controls (like, zero), and a long-running history of respecting private property. That's how they got rich in the first place and that's what makes them attractive to HNWIs who want a location where their assets won't be seized at a bureaucrat's whim.<p>After you've acquired generational wealth, your next concern naturally turns to protecting it so that it can't be confiscated at will.<p>I've forgotten the circumstance, but sometime in the 1980s (or 90s, not sure) during a particularly serious oil crises, the Singaporean government went out of their way not to seize/buy off/requisition the stock/reserves owned by refineries and oil companies operating out of Singapore. That culture of respecting private property unless the cash has a serious criminal connection is one of the biggest differences between countries losing/attracting millionaires.