> there’s probably a nontrivial amount of money laundering going on through these apps.
You can't really launder money through an app that offers no way to get money back out of it.
If there were a way to "gift" coins to people, which would allow them to be sold on sites like eBay, then you could launder money, because you'd be able to buy coins from Big Fish, and sell them elsewhere at a discount. You'd lose money on the flip but then, when you launder money, you always lose some portion of it (often quite a large portion).
(I don't know enough about these apps to know whether that's an option or not, but I suspect not.)
The only way Big Fish could be used to launder money is if they were owned by the people doing the laundering, who would then have a route to get money "through" the company. For third parties I don't think it's a possibility, unless they were in cahoots with the owners.
Actual gambling apps would provide a much better option for laundering money, which is perhaps a bigger motivator for regulation of that industry than addiction is. Or at least they would in a cash environment. Apps maybe less so because there's always a paper trail for the money (not to say it can't be done though).
Take all this with a pinch of salt because it's hardly my area of expertise but the main point stands: to launder money you have to have a way of getting money both into and out of a business.