Before 1999 an AFI could not upgrade to a FI without completing the upgrade course which comprised of removing the no applied instrument limitation from the instructor rating. Thus all FIs were qualified to teach IMC.
With the advent of JAR-FCL and the simpler requirements to unRestrict a FI rating, there was no longer a need to complete the old upgrade course which by now had become the IRI Course. In fact under JAA rules an instructor could not complete the IRI add-on until the rating was no longer Restricted. The cost of training has increased and for the average short term FI with their sights set on the airlines there was little probability of recovering their costs. So we now have a high proportion of FIs who are not qualified to teach IMC.
Now throw in economic factors and there are less customers; finally there is the EASA uncertainty however; I doubt that has had any significant effect. EASA have declared that it is not their intention to remove existing privileges and have intimated that IMC rating holders would be grandfathered into the new outcome of FCL008 whatever that might be, so I would have thought buying in on grandfather rights might have encouraged candidates to get an IMC whilst it still exists and before expensive approved training takes its place.