Aside from the incomplete picture if only tracking larger pieces, I think the other counter-intuitive part may be that there is a LOT of orbital energy before t

Aside from the incomplete picture if only tracking larger pieces, I think the other counter-intuitive part may be that there is a LOT of orbital energy before the disruption. The change in velocity applied to the debris, even though they seem significant, are small in comparison. Each piece that gets a slightly different impulse force from the event will effectively perform its own orbital maneuver, much like if they had each fired a thruster for a slightly different delta-v. Thinking of the craft as traveling "forward" along a path with "down" towards the gravitational center of the earth, a shove "up" or "down" by the impact will change the shape of the elliptical orbit but the parts will continue to travel with about the same period. They may fly "above" or "below" each other and cross paths as their elliptical orbits reach higher and lower extremes. A shove "left" or "right" will cause the plane of orbit to start rotating and lead to interesting relative movements of the parts that separate! A shove "forward" or "back" will actually change the period of orbit, so not only will elliptical paths diverge in terms of altitude, they will potentially accumulate larger divergence in each period. A real bit of debris probably has a mixture of these component vectors in its actual delta-v.