They can be, it’s just often that 1 of 2 things is apparent:
-
Builds around using them for a major or primary source of damage like the Boogermancer require getting a lot of gear with the specific proc to maximise their effectiveness and for the core stats every build needs like a diverse range of resistances, OA, DA etc… Not easy to get the equipment for legitimately. Take adoomgod’s Fireball Frank and Icicle Ivan as further examples.
-
The specific affix they’re attached to is being mainly used for the stats on the affix. The proc just happens to be an “icing on the cake” kind of deal, neat to have as an extra.