A lot of agencies produce job specs where there is no actual job, but they frequently get requests for people with a specific set of skills.
So when a client asks if they have any candidates they can instantly produce a list of 100's of them.
We recruit a fair amount (through a list of preferred suppliers) for projects and some of the candidates don't even meet the minimum criteria - which just goes to show that some of the agencies think bigger numbers are better than quality.
I also remember (early in my career) being put into a temporary DTP role for a catalogue company by my agency, and while I was there I realise they were actively recruiting for the full-time role I was temping for. Put my application in, with a letter of recommendation from the department head I was working for, and didn't even get an interview.
The girl that got the job had no background in design at all, and 'just wanted to try something different'.
Left after the 4 week stint was over and thought nothing more of it until the department head called me and asked why I hadn't applied for it. I told him that I had, and he then investigated and found out my agency hadn't even bothered submitting my application as they had enough candidates already
3 months later I was called up again, but by the line manager, and asked if I was still interested as the girl had left. I said I was, but was 2 months in to a 12 month project in Brussels on double the pay. Didn't take it any further.