Vegetation, terrain, mammals, birds, reptiles, amphibians, crustaceans, insects, most bottom-dwelling fish, most lake bottoms, even our beloved bass themselves are mostly green and brown. So, soft plastics fit right into the landscape and the biomass. That's not to say other soft plastic colors don't catch fish. They sure do. I'm certain you'll agree that blacks, purples, whites, and chartreuse are often reliable.
Smoke is yet another dichotomy.
What I mean is, you can get a smoke pepper soft plastic almost anywhere. I have not. From a manufacturing perspective, it's a similar concept in either case. Raw plastics are brought to a liquid state, injected into a mold and given time to cure. A soft bait remains supple whereas a hard bait becomes brittle.