Here's what happened:

In the beginning there were "call and response" songs - work songs, spirituals, etc.

When the blues came along, the "response" part was turned into an instrumental (usually guitar) lick.

When the blues went to the city and became electric, the lick became that much more important.

When rhythm and blues came along, the same phrasing was retained, just speeded up a bit.

When rhythm and blues morphed into rock and roll, the instrumental lick was eliminated from some songs, survived in some, and became the most important feature of others. Those songs from which it was eliminated work well sung with little or no accompaniment (e.g. Yesterday). Songs where the lick survived but was not the most important feature work less well unaccompanied - for instance how can one perform "I Want to Hold Your Hand" without the little chromatic guitar run after the first line of each verse? Songs where the instrumental lick is the most important feature (think "Day Tripper")- well, they just can't be done without it, can they?