Hi
I am not convinced that countries are banning A frames based on evidence be it factual or anecdotal. I am not convinced there has been many instances where A frames have been the cause of accidents as I am sure we would have heard of some of these instances. Todate the only one I recall was a recent event near Abbeville where an A frame was thought to have parted from the van. They don't ban Caravans or trailers and how many accidents have we heard about involving them albeit the driver usually started it. Don't say there are more of them because if that is the case there are more possibilites for accidents. We have all seen them weaving about, it happened to me at 50 on the M6. I have never felt the A frame was going to take over the motorhome.
I have towed caravans ,trailers and an A frame and the latter has felt safer to me.
Generally I suspect the reason they are being banned is concern about the modification to the car not meeting standards they and the motor manufacturer have or can approve. Caravans and trailers have type approval but I suspect they have more accidents per 1000 units than A frames do. Also as has been said it is difficult to impossible to reverse an A frame. I would say however that if you got really stuck with a caravan ad needed to reverse it any distance you could be quicker uncoupling the A frame and driving both units out of the way.
Head down waiting the flack.