This data does not surprise me at all. I occasionally ride along with groups of riders and like to have them all in front of me so I can watch how they ride. Many consider a 5000 mile bike "high mileage".
The last group ride I participated in involved about 80 bikes of mostly cruisers and baggers, mostly Harley's and included four trikes. We were escorted by LEO riders up to a veterans home just before Christmas in order to bring needed presents and cheer to the residents.
Throughout the ride, the severe lack of skill on many of the riders was sorely evident in poor cornering (on the interstate curves of all things!) inability to maintain a line or stagger position, abrupt throttle changes, etc. Through several sweepers that are easily handled at the speed limit of 60mph, several of the riders on Ultra's would slow to 40mph to make the curves, causing the whole line to collapse into an accordion situation for a mile or two. Forget rolling on the throttle. Those that did that went wide, and at least one bike managed to change lanes inadvertently in front of a large truck and not get killed.
After a mostly uneventful ride about 2/3 of the way up to the destination and in a country two-lane road, one of the trike guys managed to forget the right wheel and dropped it off the pavement causing an immediate off-road excursion through a wood fence, down and out a ditch and into the woods. His angel was present and guided him between a power pole and its guy wire (about a seven foot wide target) and into some heavy brush that stopped the bike without killing him. Damage: broken hand, severe laceration on one leg etc. and one totaled HD Trike. Happily his buddy did not have target fixation and follow him into the pile.
I basically decided that I will not participate in this run again, and will go directly up the the Veterans home. Much safer and I don't have to provide first aid gear for triage.
We had several cruiser folks take an advanced MSF class. They were riding cruisers and the reason they were taking the class was that one weekend ride, the lead bike took a curve a little hot for his skill level and did an off road cross country excursion. The three following bikes were target fixated, and predictably played follow the leader into the dirt. No injury other than pride and damaged bikes, and a realization they might need some training.
I have to say that most of the BMW riders I know have had a lot of training classes of all descriptions, and are very good riders, ATGATT and know when to call it a day if necessary. I have a few HD friends that have come to the conclusion that good riding gear makes a lot of sense and results in a more comfortable ride than skid lids, jeans, tennis shoes and T-shirts in most any condition. Some even have gone to Hi-Vis gear, to the chagrin of the black T-shirt brigades.
All that said, I know a lot of really good riders on HD bikes. They ride all the time, including some daily riders, and I have no problem riding with them, because they know what they are doing. I do tend to ride in front of them a ways, mostly to stay away from the noise (loud pipes, etc)
The other bike statistics (probably a lot of sport bikes) are not surprising either. The lack of skill seen by most of those street riders is stunning, and the real surprise is that the fatalities are not much worse than they actually are.