Because on the IMC flight test the pilot is expected to be capable of flying an ILS down to a DH of 500ft (unless the published minima are higher).
If an examiner permits use of the ILS below this height then they leave themselves open to appeal doe to how the test was conducted.
It could well be that when presented for the test they have never flown an ILS below that height.
In fact one has to remember that the IMC rating training and testing is very limited. There is no requirement to train in all the approach aids available - only two approach aids are required and only one needs to be pilot interpreted. The ability to perform a hold is not part of the test.
Only 10 of the 15 hours needs to be by sole reference to instruments. Of that 10, some can be in a ground trainer.
It could be argued that as soon as the IMC rating test is passed the pilot is firmly in the non-current and should avoid flight in IMC category.
The IMC rating has so many holes in it that making swiss cheese is impossible.
A new way is required. A rating with appropriate clearly understood limits, better sylabus and better training and testing.
Some are going to argue that it already exists in the IR but are you going to leave it at that?
Regards,
DFC