A few thoughts
Shoreside witnesses saw a person on the barge but they were about half way back and not behaving in a manor indicating they were acting as a lookout, when they saw the sailboat they ran toward the stern of the barge waving (I think) at the tug, the tug did try and stop but too late.
yes the structures on the barge sure look like impaired vision/sight lines to me and I would think that should have required a lookout at the front of the barge
What about a sound producing device / horn on the sailboat?
Was there a VHF radio on the sailboat & chase boat? Would the operators have known that commercial vessels should monitor Ch 13?
What was the course of the barge/tug? - if they were turning the sailboat might not have known they were on the intended track
The chase boat was in the process of collecting the becalmed sailboats
I am not familiar with the area but an aerial view looks like an area with probably high recreational vessel use and thus requiring extra diligence. A few years ago I was a guest on a U.S. Coast Guard Cutter that was over 300 ft long, it was traveling along the edge of a large sailing regatta with standard recreational boating, I was very impressed