Not even that; 0.1% per trade would bring in a huge windfall. Even something negligible like 0.01% would bring in nontrivial amounts of revenue.

The problem is that being above paying tax has become part of the identity of being rich, and the very idea of even a negligible amount of one’s wealth being taken away to be given to your inferiors is unacceptable, and the rich will defend every fluctuating cent of their wealth as a non-negotiable matter of honour, even if it means burning down the world.