How do you tax bank deposits while not keeping it a surprise exactly? That wealth is highly liquid, and surprise is kinda key to the whole concept. Otherwise, everyone simply puts their money in a different country's banks.
E.g. USA has worldwide tax juridiction, so it isn't an issue. In the case of France, it's estimated to have caused a loss in tax revenue, with capital flight, as there is no worldwide tax.
Actually, the tax jurisdiction of the USA is a red herring. People do renounce American citizenship to avoid American taxes anywhere in the world, just as Gerard Depardieu renounced his French citizenship. What happened in France could happen exactly the same in America, too. The extended tax jurisdiction only applies to citizens. You can renounce that in ten minutes at a consulate.
At any rate, the USA does not have jurisdiction to "tax" the bank savings of foreigners. You're conflating this bank deposits tax with a wealth tax on citizens of the same country, and it definitely is not, because it takes money from foreigners that may never have set foot in the country or used a single government service therein, or even made any income inside that country outside of a little bank interest. With a wealth tax, you can rationalize that it's "fair" to help fellow "countrymen" but this is simply absurd.
The point stands, that when you tax bank deposits, it simply doesn't work without surprise. Wealth taxes can work without surprise because most people are used to a certain culture and will remain, but bank vaults have no particularly culture to speak of.