Here's a third option to consider: the cyclist does not notice your merging in to the lane or otherwise fails to react and smashes into the back of your car. At higher speeds this can be lethal.
If you don’t merge first, you have to not only consider cyclists in the lane but also whatever may be involved with the turn itself, such as people crossing the street you’re turning into, or other obstacles.
Basically you spread the risk over time and space instead of concentrating it all into this one maneuver at the end.
Good thing this is done at low speeds. The car is basically going 0mph, because they are going to turn 90 degrees. And when I'm biking, I am BY FAR more cautious when approaching intersections. As you should be in a car, bike, motorcycle, or whatever.