A swamp is a type of wetland. They weren't renamed.

Well, there is supposedly a distinction between swamps (which are dominated by trees), marshes (which are dominated by grass) and bogs (which have a pH differing from 7). This is already kind of a weird classification scheme, since the trait that defines a bog is so wildly different from the trait that defines swamps and marshes. And then, if you believe in this scheme, "wetlands" is the generic term referring to all of them.

But 1cvmask is actually correct that the generic term was (and still is, outside of specialized scientific terminology) "swamp", and pushing the approach of my earlier paragraph constitutes a renaming.

Where does muskeg fit in all of this? Also salt marshes which while they may have grasses, are different ecosystems.

Sometimes a riparian estuary is just a riparian estuary... Let's call a fen a fen and be done with it...

Would not a bayou by any other name be as mucky?