There are few reasons for this. In the recruitment world, there are staffing agencies who have temporary, contract and direct hire openings, recruitment firms who only work direct hire and Executive Search Firms who typically work the upper end of the spectrum and are very focussed in a particular recruitment process designed specifically for their client.
When you apply to various recruitment firms and agencies, first ask what their policy is around sending your resume out into the marketplace. You probably don’t want your resume going all over the place without your knowledge. After all, it does contain some very personal information on it. If a recruitment agency/firm, is as member of a Professional Association, they must abide by a strict code of ethics. For example, in Canada, we have the Association of Canadian Search, Employment and Staffing Services ( ACSESS) and all of its members have committed to adhering to a code of ethics.
You may want to follow up with a telephone call once you send your resume in. Don’t worry if you don’t get a “live” person on the phone, you simply want to leave a message to ensure that your resume didn’t get caught up in a spam filter. Many staffing firms keep a very large data base so they can search it when they get new “job orders” in from their clients. It never hurts to apply because something might come down the pipeline later when you least expect it.