re: Tax bill has gamblers confused and mad, may still have to pay taxes even if they lose.

I think there's a third motivation no one's mentioned yet, and to me it's probably the most likely. This is specifically targeting professional gamblers, but only to remove the sharks to make easier for the degenerates to occasionally win. This keeps them playing longer, which actually increases revenues over the long run.

This has already been happening with fantasy sports. If you're a consistent winner on DraftKings, they will just kick you off the site. Similar things have happened in private poker games as long as there have been private poker games.