I have never seen bicycle delivery of illicit drugs, but there are certain guys on bikes who seem to act like supervisors over the ones standing on the street corners. Nobody is usually "holding" when they are jacked up; they seem to be acting as sales reps, and will jump into a buyer's car to take them to a crack house or other location to make the buy. Ticketing these bozos for bicycle and pedestrian violations is a way to make their lives more difficult.

Disclaimer: I do not work for the PD of my listed hometown, but for a larger nearby city.