That's the point though: large amounts of cash should not be sitting there, they should be circulating through investment. It's not a tax as much as an incentive. Inflation functions the same way by making holding on to cash a losing proposition.

There is just SO MUCH cash right now in the hands of the wealthy classes and it's just sitting there in bank accounts not being circulated.

There are actually a lot of different forms of wealth tax in the Netherlands.

What are you referring to? If anything I know the Netherlands as having a comparatively few forms of wealth tax compared to other countries, the main wealth tax is mostly based on 'one form' that is completely undifferentiated (i.e., any net wealth, as part of box 3)