The current PPL syllabus, both UK and JAA/EASA is down to Ron Campbell, who copied it from the RAF CFS in the mid 50s. The RAF syllabus dates back to Smith-Barry who introduced it at Gosport around 1917.
Like many syllabi of the time, theory was never well defined or quantified, and it has never ever been the subject of any form of training analysis. Exams were written around the text books available (initially Birch and Bramson) and later, the verbose Trevor Thom volumes, by a person who was not even a PPL Instructor! The introduction of JAR-FCL saw a few additions to the same old syllabus and questions became even more obtuse in an attempt to include ever more irrelevant items (e.g. Chicago Convention) deceided by a committee of non PPL instructors.
The JAA had 12 years to produce theory exams, but as the PPL was never meant to be part of JAR (AOPA proposed that it should be) it was never in their original plan. Having seen their attemt at proffesional exams, it is probably just as well they didn't. EASA now propose numerous ill conceived and totally unprepared new licences for different aircraft categories, at two different levels (PPL and LAPL) yet there is not an examination question in sight, neither is there any intention to produce any.
What we need is theory that reflects the practice at both PPL and professional level however; the chance of any change in the near future is Zilch. The CAA no longer employ any experienced ground examiners, EASA has none, and organisations like
LPLUS are producing irrelevant junk at the professional level.