I just got an answer to a question I posed to a MO Fisheries Programs Specialist some time back. A MO website said: "Missouri's numberless farm ponds are bulging with fish. You can...throw out a worm for almost any species." I asked, why not pickerel? And his reply is:

"Pickerels prefer rivers and streams and will not thrive for long in ponds. The habitat and food sources in ponds are not what pickerels need, and they are outcompeted (and preyed upon) by largemouth bass."

I guess he was telling me why they don't survive in ponds rather than why MO won't allow them to be stocked, but I think there's ample evidence that they do survive in ponds.