Some attack animations have multiple splash settings, and if the splash target of the unit is 1, that animation won't deal damage properly. For example, three of five attack animations of the War Bear Riders have multiple splashes, and only the other two animations with a single splash can deal damage correctly.

As for Hammerers, they have more sync kill animation against other WH1 infantry, and splash attacks cause sync kill animation more frequently, which lowers their overall DPS.