Pure inexperienced rider error.
Harley rider had NO idea of his motor's handling limits nor of his own.
He had plenty of lean angle and time left. The rider was merely too inexperienced to know how to utilize it.
I do not wish to begin an argument here, BUT according to my training and nationally renown motor crash experts, there is no such thing as target fixation.
Granted one seems to move in the direction he looks; however, there is no phenomena that freezes the actions or locks the gaze of a rider onto a particular object.
This was a human factors issue dealing with lack of proper decisions resulting from the poor skill set of the rider.