Where there is money, expect scammers to lurk around, too. Bitcoin is value. In this forum you can make lots of money through different deals, trades, services and carrying out tasks. So I am not surprised that we have so many scammers here, and it is not just Bitcointalk. They are in other forums too, and it's even worse in some. At least here in Bitcointalk we do have the default trust and flag system.
I don't think there is always someone introducing new scammers here. Most of them are probably old scammers who have been busted, and they just create new accounts.
Where ever we go in the forums or in the real world there are many scammers who actually want to us to be Their victims so we need to vigilant and double our security inorder to prevent such mistakes. Agree with this mate that those newbie account they are scammers it's look like they are not totally newbie for sure they are old scammers like what you said that maybe they got banned because of their doing then now they create a new account. And act like they are a new one. So everyone of us here need to double our security.