Becuase the trailers are really trash, its handling is really bad and it turns over every 500 meters. For the record having a longer trailer is immediately going to make trucking harder. From my knowledge nothing has changed handling wise from the old trailer and new trailer, only physics did as we now use one that's longer and has more space between the axles to the rear of the truck. Trailer haulage isn't an easy skill for a driver to learn, but of course it depends on the trailer that you've got attached. I suggest you slow down and take it easier on turns, don't go past 80 on turns or you will actually have the trailer drift all over the place. This is again because of the length of the trailer and where the axles are located. The trucks are also meant to cap at 120 or 140 if my memory is correct, so please drive responsibly as it's not meant to travel its max speed (or have v8) unless it's going in a straight lane.