What a strange slide, was it rainy or cold? Both? Seems like the trailer was either fully loaded or overloaded but the truck wasn't loaded much at all. Trailer brakes could have helped but I don't think they even hit them. They were definitely going too fast for their load, regardless.
Edit: I don't see any water on the roadway so I guess wet is out.
I think his trailer brakes were out ot non existent. He looks to be hitting his truck brakes while turning which really works your tires (changing speed and direction at same time). Whole braking the trailer was pushing on the back of his truck enough to overcome his tires friction.