Can you imagine the fights, chaos, screaming on the vedder, if in addition to a bottom bouncing rig, everyone decides to do some float fishing with their "other" rod? Or why not throw in a little bar fishing.
Like someone said before.. the shoreline is a more scarce and therefore potentially crowded resource, which only makes sense that you need to limit things, as opposed to the giant blue ocean.
Also the shoreline, riverways, beaches are shared with non-fisherfolk, so again, to limit the impact of fishing makes sense once again.
And finally, the fact that a river, stream, lake and tidal flat is smaller than an ocean (with smaller populations of fish) it only makes sense that the ocean can stand the added fishing pressure of an addition rod.
End of discussion.. fish one rod.. and sorry.. but NO to groundbaiting for carp...