As far as I know, the only landings in France were Operation Overlord and Operation Dragoon, both of which took place in 1942. Could you please tell me what I'm missing?
I agree that amphibious landings are very difficult just to plan, much less execute, which is why no landings after mid-September were seriously considered by either side.
But the fact that something is difficult has never been an acceptable reason not to do something in the military. It's not whether it's difficult, but whether it can or cannot be successfully done...and if the Allies didn't do something they could have done, there was a reason why.