Once in a (great) while, authorities go after one of these guys for tax fraud or other financial shenanigans, but as far as their other claims go, they probably fall under a broad definition of religious expression. As Senator Chuck Grassley found out a few years ago, if you even try to take these people on, they start screaming and yelling about religious liberty, and other mainstream religious organizations and conservative groups will chime in to support them, or express "concern."
Maybe the government can't do much, but I think the mainstream media should be doing more to expose these scam artists and bring them to the public's attention. But I guess they're afraid, too, religion is too much of a hot potato...