Pokedex entry for Grimer: Grimer emerged from the sludge that settled on a polluted seabed. This Pokémon loves anything filthy. It constantly leaks a horribly germ- infested fluid from all over its body.
Therefore, from man-made pollution.

Pokemon are not based on Man-Made objects?
Magnemite. Magneton. Voltorb. Electrode.

And by the way. under your own standards, the Vanillite family is justified, since they are not ice cream, they are living icicles that cover themselves in snow for camouflage.

>Actually replying to an obvious troll