cwatters
Not dissimilar to the way in which a thermal will boost one wing and give you the "net" effect of an unwanted roll. If you've ever watched a dust-devil accelerate away from the ground and broaden out as it gains height and entrains surrounding air, well just imagine the wake vortex to be a horizontal thermal that is similarly expanding as it drops astern. The essential difference is that the thermal is accelerating and the wake vortex decelerating. When you hit a wake there will be a net effect upon your airplane ... BUT it is also true that part of your airplane might take a fairly direct hit from that rotating helix. That didn't seem to matter in an all-metal airplane. When it's a large vertical surface that's not really designed to take large thwartships airloads (because it's made of composite material) - well that's apparently not immaterial.
My theory (at that url above) is that if you take that hit and it causes an FCS overreaction (per the reasons and sample incidents given), then the combined effect of rudder response and an ill-timed second wake encounter (from the other wingtip's trailing vortice) may be a sufficient overload for failure.