OK, if you want to play it like that, let me start by challenging a couple of assumptions.

First, the relevance of linking loot boxes to problem gambling. Ultimately gambling is not illegal, so this doesn't inherently suggest that the situation demands new legislation. The worst case scenario here is loot boxes are made analogous to gambling, which is presumably already as regulated as it's going to get on each territory. There's a lot more to question there, as there was on all the frankly sloppy analysis on the links of gaming to violence in the 90s, but there is an implication at the core of the attempt to link them in the first place that I don't think is justified.

Second, I dispute the need for them being on the wane predating your gate for legislation. For one thing, you're not being explicit about when "regulation" by your definition starts. By the way you've sourced it you can arbitrarily choose any point in time. For another, it makes sense that regulation and self-regulation would happen in parallel. Ultimately bad PR and negative research motivates both public and private action. Again I refer to the 90s violent game panic. If the probes on gaming violence motivated the creation of age ratings agencies for gaming, does that mean the age ratings weren't enough of a mitigation and they should have deployed anti-violence legislation? I'm going to pretty strongly argue that's not the case.

Also, I feel you're misrepresenting the metastudy you provide on the results of self regulation. High compliance/high effectiveness is the biggest segment on all counts. Granted, on roughly half of the studies, but a lot more studies find self-regulation to work than not, by that metric. Why is "a small but replicable correlation" such a concern but a majority of studies finding self-regulation is highly effective a mixed result you don't trust? Seems to me you're not treating all the references you're using the same way.

FWIW, I find this conversation not particularly productive because, frankly, with these things the literature gets to be a huge mess. Again, my reference is the 90s violence campaigns, where so many terrible papers were being funded and published the academic conversation became entirely impractical. The fact is gaming did need some age ratings standard and it made sense for national agencies to exist to manage them. And it makes sense for those same agencies to have explicit policies not just on loot boxes, but on all in-game monetization. The industry needs best practices and safeguards. And the public, incidentally, needs a LOT more awareness of why self-declaring age in accounts is important and what safeguards are already in place as it is, because there is a ton of parental control and underage protection that kicks in but nobody is particularly aware of it.

But instead gamers whose concern with loot boxes is primarily artistic have been rooting for overreach in hopes the result is games they like more. I find that risky and problematic, and the idea of Brazil's government passing wide-ranging age verfication regulation and having English-speaking media and social media report on it based on a mostly reasonable mandate of loot box games carrying an 18+ rating more concerning than any of the underlying issues being addressed.