Your statement makes it seem like you think that guys who come from the schoolhouse haven't flown the line or don't have an intimate understanding of line flying. Personally, I flew the line for 10 years before taking a job as a flex. Getting hired for any position in management or training puts the individual through a thorough screening process, during which any number of things, including just one negative input from another manager or LCA, can preclude being hired. Knowing this, it might make it a bit clearer why pilots who are already LCA/Flex instructors are sometimes more easily placed in management jobs. Not to mention the obvious fact that guys who are willing to do the extra work and have proven themselves over time to be strong performers in the training arena make them obvious choices over an unknown entity (who might be equally qualified, BTW.)

Put yourself in SJ's shoes and decide for yourself who you'd hire...a guy you had worked with who had an established reputation; who had been endorsed by guys you knew and respected, or an unknown line pilot whom you had never heard anything about.