God created weed because there has to be a natural balance in the world. If weed didn't exist wouldn't you imagine a small weed sized hole in the earth's equilibrium between good, evil, medicine, drug-use, controversy, peace, etc...
Or maybe there is no god, and it's complex genetic mutations that created weed, or it came from a comet from another planet that was destroyed when it's galaxies sun collapsed and somehow it made it to earth's gravitational field.
jk luls