Jamb movement loosens fasteners
On a door this age, that cycling works on two fronts: the wood jamb the track bolts into swells and shrinks, loosening fasteners faster than in a stable climate, and any galvanized coating on the original track has usually worn thin enough that surface rust has started pitting the rail itself. A pitted track doesn't hold a roller the way a smooth one does, even after we true up the alignment.