Like technological and social disruptions, I think usually the difference is that the new thing has a different agenda than the old - different goals. As a result, the old can't make sense of it - by their goals the new thing is obviously worthless. To the market-dominating Blackberry phone maker, obviously their phone was far superior for email, so why would someone in business buy an iPhone?
My working theory is that the new thing 60s rock'n'roll aimed for was personal expression. Vaudeville acts weren't expressing things about themselves (very much - it's always a matter of degree). There was no 'Let It Be' moment, or expressions of aggression or deeply felt love. Vaudeville and a lot of the pre-Beatles pop music was (very generally) entertainment, not so much art. Look at jazz too, going from Ellington to Coltrane. Look at the rise of folk music. 50's crooners mocked the singing voices of rockers because that was their goal - an aesthetically beautiful voice; they perhaps didn't see the point of rockers was personal expression.
Again, that's speaking very generally. There were many beautiful voices post-Beatles, and there was self-expression before them, and the dividing line isn't perfect.
Now it seems to me that we are leaving behind personal expression. If true, I think partly it's an outcome of culture wars: it's associated with liberalism, so many reject it; and real personal expression can be uncomfortable and non-conformist, and that's divisive and provocative to many. But I am building speculation on speculation.