So, what happened to loot boxes since those games? There was public outcry, and publishers responded by scaling back loot boxes. That's essentially the definition of self-regulating.
No they didn't scale back loot boxes as they're still in every other game they were forced to make the two games playable with out them that is not self regulating that is a prime example of what I pointed out in seeing how far they can take it and getting caught another example is Destiny 2, fact is these 3 games highlight that the is no self regulating like you claim because it took a massive shit storm to have the underhanded practices that forced people to buy loot boxes removed.
This is why Governments are now stepping in because the industry has flat out shown they're more trying to see what they can get away with than regulate itself, the law doesn't have to state it has to regulate video games it regulates anything that can fall under a certain category regardless what the product is so loot boxes being a gambling mechanic can fall under gambling itself which is a category that requires regulation.