Normally an Edwardian woman did not expose her neck during the day. As high necked blouses gave way to a new fashion for slightly lower necklines the velvet choker appears. One can only speculate why this relatively short lived fashion came to be.
Perhaps because the bare neck presented an opportunity for adornment not available before or something was required as a transition from a covered neck, to a bare neck.

Above photograph by Lytton &Co of Sheffield •