> I do not see how anyone could make money unless they play ball with the big companies

One way is to play ball with the candidates. A big casualty of the job search is the candidate because they deplete their savings while looking for a job. Companies on the other hand can afford to not spend the money on a hire, or delay hiring, or put job postings that aren't really hiring to keep up pretenses or as marketing or feel they're not losing anything. The candidate doesn't have a concentrated force to counteract this.

If candidates wised up it could get interesting. A web app that is the other half of LinkedIn could be there waiting to be discovered.