Aspect of Salt greensteel is Water + Negative. Not that such weapons were ever all that common to begin with, but once Harbinger of Madness pack was introduced, I do not see why anyone would make them at all. Compared to getting 24 Larges, running the chain a few times to acquire Polycurse Dagger takes very little effort. Moreover, a lot of mobs are resistant to cold and negative damage, but not to the dagger's curse effects. Granted it is a dagger, and is good mostly for TWF types, but a caster or a THF probably never went for Corrosive Salt weapon[1] anyway.
[1] Corrosive Salt accessory or DT armor is a different story, and remains viable