The first difficulty is technical: keeping such food dry requires a moisture barrier, or it will absorb water from the air. There aren't many materials that will do that, and biodegradable plastics, or the waxes in waxed paper, don't biodegrade very well (if at all on the ground). Other degradable plastics won't last the expected long shelf life. That's not to say it's not possible, but the second difficulty means there's no real market for a more expensive biodegradable solution.
This second problem is human: the people who care about not littering would take their rubbish home either way, and those who don't care won't pay a premium for it.
Finally, one solution doesn't fit all: waxed paper might be the best solution in some cases as it's cheap and can be burnt (in fact used as a firelighter), but if campfires are forbidden it has little or no benefit. It would however be a good material if making your own dehydrated meals.