In an ideal world, that would be the case. However, someone has to coordinate things; negotiate contracts with clients, keep a database of qualified (or not) crew, update that database, arrange transportation, accommodation, medical coverage (when provided), have standing agreements with training companies, fuel providers, etc., etc.
Few, if any, clients would be prepared to negotiate each and every contract with an stream of job-seeking pilots.
At the end of the day, the 'services companies' do a necessary job, and, in many cases, justify the extra 20-30% charged to clients. The thing that distinguishes them, though, is the way they do the job. Some with professionalism, good humour and a desire to things the right way. Some not.
A bit like pilots, really.