Driver knew he'd been hit, but drove less than half a block to park in his own driveway... not exactly leaving the scene, but... huh. Guess he just wanted to get off the road.
Driver didn't look in the back of the van at the shattered glass. Might not have realized it was a motorcycle that hit him. Who would think of someone coming through the window.
As for the rider not being able to stop in time... bike v minivan brake systems... to hit with enough force to be thrown into the van, I'd say the rider was 50% or so at fault here. Maybe speeding, not paying attention, or some other contributing factor.