That's like asking why people throw spinner baits in the east. It works!!! Besides, you are still patterning the fish when you drop shot. Take this for an example: I was out at Pleasant a month ago and couldn't get any of the bass I was marking on my graph to take a spoon or crank or whatever else I through at them. These fish were just innactive. So, I fired up the motor and headed to a different spot on the lake when I came over the end of the point and noticed the bass/shad were scattered. So I went back over the point and through a crank, spinner and so on. Then I switched to the drop shot and found that these active bass were holding on the side of the point facing the wind and that they wanted the bait to barely move. From there every time I came up to a point I fished the windy side in the same way and kept getting bites. That's patterning bass, it doesn't matter what technique you use.
-Dave King