That's not to say that its taught very well.
Bit of a sweeping statement that, Whopity.
When, as CFI, I redesigned the PPL course for the Club at which I flew, we integrated all aspects of Ex 18C into the navigation phase - including VDF, radar, VOR, DME and ADF. I also included the requirement for students to have passed the Navigation, Meteorology and Flight Performance and Planning exams before their first 'real' navigation exercise.
All our aircraft had panel-mounted GPS, so I also included a note stating:
NOTE: Before Ex 18 is flown solo, students should be able to read their present position from the GPS.
Not for navigation, but to assist if they became uncertain of position when solo - at least they could then report their lat/long to an ATS unit or London Centre.