I covered this in my initial post. That doesn't seem to be what happened. Tons of people who were suspended claim to have had their gil reduced by 99%. There is absolutely no way that 99% of the money earned by the richer player accounts were made by selling to "criminals." What seems to be what happened is that a large number of gil entered the economy through methods unintended by SE, and as a response SE swept up many of the richest players and reset their gil.
Imagine if, in the real world, a large number of counterfeit money was introduced into the economy. As a response, your entire bank account, and the bank accounts of a select group of others, got reset. Maybe most of the money you made actually came before the counterfeit money was introduced. Maybe some of the money you made came from working an honest job and you know for a fact it isn't counterfeit (in game, this is the case for people who made a chunk of their money from quests/leves and still saw their entire wallet go up in smoke). In this situation it wouldn't matter. Money got introduced, money got taken away, everything goes back to normal for everyone accept the people who were cheated out of their savings for a quick fix.