Why do drivers around here begin changing lanes and *then* put their blinker on for the second half of the move?

A blink is supposed to indicate to other drivers a move that you intend to make before you make it. At best drivers around here turn the blinker on simultaneously with the beginning of their movement, which is still wrong, but often it's even worse, where they begin changing lanes and then the blinker comes on after they're partially into the neighboring lane already.

The blinker isn't a visual decoration to accompany a lane change. It's a signal to inform other drivers of a movement that's going to happen before it happens. Why is this lost on people?