But that doesn't mean that people can't be found to be untrustworthy if they promote such schemes. You can tag and open scam accusations against them for all you want.
It is just useless. My account does not have enough opportunities to blame everyone for cheating. And the majority of newbies will go over the signature of respected participants and plunge into shit. This forum has millions of dollars in cryptocurrency and a lot of opportunities, but it is more profitable for them to cover fraud.
Anyone can bring up an accusation and if it's valid it has "opportunities" to be supported by DT members using flags and red trust ratings. That's what happened to LiveCoin recently.
The system is not perfect but expecting forum staff to moderate scams - while it may seem like the right thing to do - would likely end up with a lot of issues too. For one, you can't expect them to find every scam so you would still need to sort of community reporting/policing option, which is essentially what DT does.