Why Are Contracted And Outsourced Workers...

Why are contracted and outsourced workers not the largest group in all organisations, especially considering one of the major aims of HR is labour flexibility?
I am aware of Atkinson's model here. Any knowledge or links for me to research are appreciated.
Thanks!

my random thought would be "job commitment', organisation would want certain percentage of job commitment from employees, and with a contracted labor pool, that may not be possible.
On the other side, a contract worker would essentially want to get job permanency .
I wasn't aware of the Atkinson model till now, did a brief read and found it interesting.

Hi!
In some countries, job contracting and/ or outsourcing is regulated by law and can only be done for jobs/ functions that are not integral to the business of the organization.
The outsourcing of integral jobs in an organization to third party manpower providers or independent service contractors can violate laws, especially labor laws.
In our country, the outsourcing of integral jobs is prohibited by our Labor Code. It is branded as an "illegal job contracting" because the suspected intent is the avoidance of benefits payment, absence of job security and tenure, and/ or union busting.
Best wishes.
Ed Llarena, Jr.
Managing Partner
Emilla Consulting