I have pointed this out before but can't now remember whether here or somewhere else, which is a trifle embarrassing
However that quote of Uncle's explains to only part of the problem.
Yes the exam boards are in business to make money. They also run courses which teachers attend (at a price) to show the teachers how to get their charges (pupils) through the exams. Many schools that enjoy "Good Results" are the same schools that are willing to pay to send their staff on such courses. The whole system has long been corrupt .... one such "Examinations Board" has as it's MD a member of Offsted. Another is run by a leading light in a Teaching Union and all have close connections with leading Government Officials responsible for Education.