Things cyclists should know … POV driver who's incapable of cycling

but on a bit of road, as portrayed in this pic, why is it necessary to cycle in the right hand half of the lane?

well I can't see what the cyclist can see, or feel, but I would suggest one or more from a list that could include
approaching a:- junction on the left

                        parked car
                        slower cyclist
                        pothole
                        pedestrian about to step off the kerb
                        child
                        dog not on a lead
                        swan
                        bus
                        dustcart
                        turning right
                        roadworks
                       roundabout
                       pick up truck with blacked out window

or is affected by low sun, cross winds, tiredness, aspergers, a sneezing fit

and so on