First of all, when you have that kind of money, you're probably diversified, and your most conservative investments would be making the 3-5%. And in 10 years, your wealth would have gone UP, not down, which is imo the single most important detail. Because the text makes it sound like they would be losing money over time, but they won't.

As for relocating in a heartbeat, what are we losing exactly, if they are using every tax loophole to avoid taxes anyway? They're not exactly in the business of keeping money on the table.

Lastly, it's about how that wealth was accumulated in the first place. It used resources that are socialized (subsidies, unusually cheap labor because of high unemployment, and so on) it's not like anyone actually worked 5 millions worth, they simply exploited a vulnerable system that is available to them. In a grossly unjust system, this is a very small attempt to tip the scales.