That was done for military strategic purposes, not simply for the lulz.
It probably only really happened for the lulz, as a ceremonial curse.
They didn't have (literal) tons of salt to waste on spite.
Symbolically destroying small amounts of resources and depriving yourself and family of a clean environment to essentially complain. Hmm maybe scorched earth is the better description of whats going on here? Salting the earth is done by the aggressor, scorching the earth is done by the retreating party. I think it still fits.