I listen to quite a lot of radio 4 but listen less because of spotify, availability of podcasts etc. If there has been a drop (and I cant see evidence for that - radio listening increased due to pandemic from what I remember) then it is likely due to the increase in alternatives particularly the increase in non music based programmes.
Good Morning Thursday 25th April 2024
Gary Glitter programme Tuesday
Elderly fellow gran has become loudly racist
Washing bio gel or quid in the drum
To think that London, or anywhere else for that matter, does not belong to any one demographic