Why have there not been any new tilesets?

Is it impossible to make custom tilesets for Warcraft 3?

Impossible? No. Tedious, I think. I've never tried it myself, but I don't think it gives the same satisfaction as modelling or unit skinning does.

No, its possible

To make a new tileset you have to make the variations and so and so yourself then import it over the already existing Warcraft 3 ones.

"Why have there not been any new tilesets" Blizzard wont help you here, and i think the chances of finding a tileset up for grabs here is pretty slim, but nevertheless, it is possible, just really, really tedious.