Because there are none. Each FTO submits a course for approval that they believe will cover enough areas for the candidate to pass the test. Most courses are roughly the same as the information is shared around the industry.
When I wrote my course outline I was given an example guideline to work from and had to populate the rest myself. The same thing when I wrote training, ops, quality and SMS manuals.
It's a bit odd that the theory is very clearly laid down but the practical is very wooly!