Bicyclists think they own the road. There may have been a time when bicycles and cars could share the road equally, but we live in a time when cars are the main mode of transportation and bicycles have their own designated area on the side of the road that is wide enough for cyclists to safely ride single file. But for many cyclists that is not enough.
From my experiences while driving on Saturday mornings, a popular day for bicycling, cyclists feel the need to be kings of the road.
When provided a striped lane, they don't ride on the side closest to the sidewalk or even in the middle. They prefer the edge closest to the white line, or even right on top of the line.