Probably the damage stopped at reinforced areas, having started between say reinforced pillars after damage/lack of maintenance and could still fail due to what is happening either side.
IIRC most large dams are built with the ""wall" including the sluices between two or more supports, longer/wider ones often have multiple sets of sluices and support sections (which may contain equipment to operate the sluices).
A google of the dam from before suggests that there is a change in construction (probably the operating house) on one side of the damage, and that it looks like it's basically lost a number of the supporting pillers and probably stopped at a (for now) undamaged/intact one.