The advertisers know they are purchasing CPM ads and are therefore untargeted. If they have any knowledge at all, they must realize that this is not a very effective method. The thing that is attractive is that it's a very cheap form of advertising. Many people will start with that sort of thing, hoping to get a few click-thrus and then sales to start out with before buying better forms of traffic. It starts with all the people jumping into any kind of online business without a clue to how to run a business - like startup capital, advertising budgets, etc. It can be done but it's like rowing your boat upstream.