Its simple, but wrong. Hence the papers remain full of ads.Craigslist and similar are representative of how the nature of advertising has changed and how much of it has shifted online. It is a relatively simple argument in that online advertising is gradually overtaking print advertising and other forms of advertising with more precisely targeted (behavioural targeting) advertising that is generally more economical for the advertisers and more efficient at targeting the users.
You are mixing up me going onto a site that is advertisements and me buying tat on facebook. The latter is not a great investment for FMCG. The pull out supermarket suppliment is.