Not many details have been released yet. But photos show a serious accident between an SUV pulling a trailer and a couple of motorcyclists.
Stopping distances are increased when a trailer’s involved. Also, there can be control issues (like jack knifing) that aren’t in play when a trailer isn’t being pulled.
It’s the responsibility of the driver pulling the trailer to provide an extra margin of safety to ensure that they are able to slow down in response to changes in traffic conditions (like motorcyclists pulling onto the roadway).
Accidents involving motorcycles and trailers require (or are best handled by) attorneys who have focused experience dealing with both accident reconstructionists and the special characteristics of the vehicles involved.