Just wanted to point out that some companies post jobs only through recruitment agencies. For one job that was being advertised through a recruiter, I figured out the actual company that was hiring, but when looking at their own website there was no information about the position whatsoever. My current role was also advertised through two recruitment agencies, but not by the company.
This seemed a bit odd to me at first, but it seems they were looking for a particular type of candidate. By working only with recruiters, this company was easily able to screen applicants before they even considered their CVs.
For one particular role I'm thinking of, I applied and so did a colleague of mine-- but he was considered and I wasn't, simply because (on paper), he was more focused on chemistry, where I was a bit more diverse and had also worked in biochemistry. Apparently I wasn't the type of candidate the company was looking for, so was screened out at an earlier stage.
I do think the use of/dependence on recruitment agencies varies from industry to industry though, as my partner has never used one.