To protect the jobs in professional flying schools, and to protect the jobs in the CAA which gets fat fees from licensing these schools
I half agree. I've no doubt the large school lobbies had a significant hand in JAR-FCL. However, the regulatory bit I disagree with. The JAA system, and to an even greater degree, the EASA system is based on a European ideology around "Organisational Approvals". In this model, the regulator's role is confined to a higher tier of overseeing organisational systems and processes and then trusting those approved organisations to do the rest pretty autonomously. This works great for the airline world, where the training and maintenance organisations are inherently large scale. Of course, it's hopelessly bureaucratic for the more fragmented world of GA, where a good independent engineer or instructor can deliver results just as well or better than a bad approved school or maintenance outfit. However, it results in fewer regulatory jobs, because it takes far fewer CAA people to approve a few schools than it does FSDO inspectors to oversee the independent operations of many instructors and examiners in the equivalent in the FAA.