This so-called 'process' was an historical accident, born of a time when oral transmission (along with its attendant risk of 'Chinese Whispers Syndrome') was the only form of song distribution.

So how come it has now become a 'rule' to be applied to modern compositions, for which a myriad of alternative transmission streams is available?

It's akin passing a law whereby all new motorways must have built-in wagon-wheel ruts. Stark staring bonkers.