There have been cases of the CAA refusing to issue an FI rating because the candidate has no evidence of a pre-entry flight test. At that point it gets a little daft but its not an option it is a mandatory requirement. You are probably lucky that they issued your rating, I'll bet the FIC instructor got a kick for it.
If you had conducted any FI training you would know that not all CPL/IR holders are suitable candidates to become instructors, so you need to know what you are taking on before you start; its better to turn someone away at the beginning than halfway through a course. Just because you passed your CPL skill test yesterday doesn't guarantee you are suitable to do an FI course tomorrow. No FIC instructor is going to waste their time taking on unsuitable candidates. The Pre-entry test is an essential precursor to an FI course and to suggest that its a way of making more money is totally naive.
The examination of FI candidates is independent, the FIE who conducts the test cannot have conducted any of the training. FIEs work for themselves not a school. CAAFU has not existed for over 14 years!