The problem here is that all these barges had to come from somewhere, and in fact they had all been collected from the French, Belgian, Dutch and German river and canal traffic, from the Loire, Seine, Maas, Rhine, Ems, Weser, Elbe, etc. systems.

At the time this carried a large volume of goods in waterways, and today this is still very important. The fact that so many craft were immobile in the Channel ports (and subject to the attentions of the RAF) was already causing strain to the economies of these countries due to paralisy of transport means.

Of course later on the Allies had the time and means to build a dedicated fleet for the purpose, naturally the Germans had to improvise and get whatever craft were available from the civil economies, with bigger or lesser consequences.