EASA have stated, officially, that the justification for retaining the CPL theoretical knowledge requirement for PPL instructors is because it is required under ICAO Annex 1.
This was the argument put forward by the Belgium national aviation authority which, ultimately, EASA acquiesced to.
There are a number of things wrong here.
First, it has absolutely NOTHING to do with flight safety - EASA's primary remit. Why? Because the LAFI rating to teach the LAPL doesn't require the CPL theoretical knowledge requirement, so clearly EASA doesn't see the CPL theory requirement as a boon to flight safety as it pertains to instructors.
Second, to date, the differences filed against ICAO Annex 1 is larger than the Annex itself, so any excuse that they have to toe the ICAO line is specious, to say the least.
Third, in my opinion, instruction should not classed as aerial work - which is the ONLY justification I can see for the CPL requirement.
The Basic Regulation MUST be re-written; EASA must be properly funded and staffed, and if these ridiculous new regs are to remain then they MUST be written as soft law - i.e. written in such a way that an 'alternative means of compliance' can be filed by our CAA. If these regs are put into hard law then only European Parliament can change them.
Regards, jez