That might have been true about a year ago, but I've been getting calls from well-spoken native-level scammers for about two months now. They are so frequent that I can put them on speaker during family gatherings to raise awareness.
Sample sizes of 1 are never representative but they definitely have full access to native speakers or tech that can generate very passable speech.
It seems quite possible that the change you've seen in these last two months is because some have started using these models. More likely than a sudden huge shift in either the country of origin or English skills of the scammers.
My point is that these models were already out there before StyleTTS2 was released. Plugging your ears and demanding their regulation in your country will not make them disappear.
Sample sizes of 1 are never representative but they definitely have full access to native speakers or tech that can generate very passable speech.