This does sometimes happen. I replaced the coupler on my parents' KitchenAid (same mechanical design as your Kenmore), and it broke again about 1.5 to 2 years later. The latest replacement couplers have a metal bushing which should last longer. An improper install can cause early failure, but coupler replacement is a common repair, doesn't seem likely an experienced servicer would have a problem with it.

Heavy loads (large throw rugs for example, Mom did say she had washed a rug prior to the recurring incident) can cause the coupler to break. Washing shoes is also a common cause, they get jammed between the basket and agitator fins. If none of this applies to your use of the machine, and the coupler breaks yet again within a few weeks or couple months, I'd suspect a developing problem with the transmission. Two years, not so much.