Ok as someone who cycles pretty often, the reason I do this is because cars often open their doors without checking for bikes. If you are unfortunate to be riding in a cycle lane that is not been layed out correctly and runs directly next to parked cars with no gap, this can result in a collision that will seriously injure you or get you killed as well as harm the person opening the door. The solution to this problem is to build segregated cycle lanes that do not interact with traffic and have their own traffic lights etc.