I bet the majority of their operating budget is people who drum up the contracts/relationships with these companies.
It's one of the biggest things you can't automate and there's a certain kind of person that fits this role. These people reach out to companies, find out if they need work and would be ok with these kind of employees and then they have to work out an agreement. It's very personal and very human.
As explained elsewhere, our staffing business was by far our best product line. Staffing is a notoriously people-hungry enterprise. They're required to sell large employers, nationally, to handle the logistics, to drive job-seeker acquisition, and much more. This is not a pure tech undertaking.
Not everything, particularly employment, can be self-serve through a website.