I still keep wondering why even pretty good bands so reliably founder on Beatles' covers.
Maybe it's as simple as this:
- Because of their experiences in Germany, the Beatles were one of the best live bands in rock history,
- When added to the complexity of their melodies this sets a very high bar for covers,
- George Martin's production then adds a feeling of canonicity to their specific performances.
So then when you cover the song it usually sounds like just a bad copy or something different but not as good.