dddd

When a right bearing cone self-tightens (as also sometimes happens on a left pedal), both bearing cones and cups are equally affected, but the right cup may be the first to shatter because it sees additional loading even under normal use.

These stamped cups are hardened after being formed from steel sheet, so can be relatively brittle, and are poorly supported within the hubshell's simpler cyclindrical-shaped bores.

I have re-installed stamped cups which became loose in the hubshell, using Red LocTite to very good, long-lasting effect.

Another cause of an over-loaded cup like this is when a mechanic attempts to loosen the outermost driveside locknut while perhaps holding the cone stationary.
A second driveside locknut may then be preventing the first locknut from turning free of the axle while the cone gets driven hard against the driveside bearing, thus overloading both bearings and literally re-forming the ball races deeper into the shell (I have to admit doing this once a few years back).

Again, these stamped races are not supported by solid hubshell metal along their outer ball radius, leaving them vulnerable to collapse.