thrash is trendy in the US now. The whole retro thing is very hip.
The same thing is going on in hip hop. Groups like the Cool Kids, kids who were not even born back then rocking 80s gear, dressing like Back to the Future extras and buying members only jackets on ebay for 200 bucks.
I'm not saying that there's anything wrong with teens listening to Razor and Xentrix, it's just that the music of bands like Hatchet and the like doesn't sound that sincere to me and looks like a bunch of bandwagon hopping to me.
Municipal Waste are definitely an exception to the rule though, I think.