>>43831225They come up with designs for Pokemon first, then flesh out the stats, typing, moves, in-game stuff second. Remember, 5/6th of Pokemon's money comes from toys and merchandise. They make designs that sell. It just so happens that none of their designs so far fit into those categories.
Also of note, many of the types you listed are polar opposites. Things like Fire/Grass don't really make sense. What would it be? Some sort of Ent that's on fire? There's a reason why we get basic, common, ideas like Water type that looks like a fish every gen.
