Its all about the money. As long as there are suckers to buy stuff, there are advertisers willing to pay to get their product on the networks. You have to be pretty bad for a network to turn down advertising money. You think the scam sales are bad? American news agencies have no legal obligation to tell the truth, so they can just about make up anything, or exaggerate, and stretch truths as much as they want to get you to watch the news (short of slander).
As long as they don't get sued they will gladly sell their advertising time to whoever will buy it. That is why on those infomercials, there is a disclaimer about how the TV station doesnt endorse or guarantee any of the claims or products featured. They only care about making money and nothing else. It shows the inherent disconnect that lawyers have created between what is legal, and what is right.