I have heard that the theory of "wet foot" or "dry foot" is used when determining if someone is allowed to stay and ask for asylum after being captured by the coast guard.
If you have a "wet foot" as you would if you were swimming to get the US, it is ok. If your foot is dry, you are deported. So, many on board boats jump overboard, so they will have a "wet foot". So, is the issue one of semantics here? Wet back? Wet foot? What is the difference? It means the same thing; it is someone trying to get to the US illegally.
I think you have that backwards. Wet feet will get you deported, while having one foot on dry land proves you've made it to the US without any kind of government help & allows you to ask for santuary. It only applies to Cubans. They jump out of boats in the hope that they can get to shore before they are caught. If you have numerous people swimming in all different directions, it's more difficult to catch all of them than it is if they are all together on a boat.