From facts I gather from the news;
A number of riders entered the road 500' from the accident scene traveling the opposite direction of approaching pickup/trailer swerving into their lane.
sadly, numerous riders down from collision with truck/trailer. Feel bad for the families, so tragic.
My opinion, for what it's worth:
Driver 25 years old, not sure how much experience driving such a rig and betting a too short time to brake effectively causing swerving trailer.
The large number of riders entering the roadway from hotel as a pack caused vehicle(s) coming from opposite direction to apply brakes. Long chain pack riding (side by side) usual MO from MC group caused obstruction of opposite travel and the bend in road.
Unfortunate, but both sides may be at fault.
I've been riding for 30 years, and just get a little annoyed in these long chains of riders acting as one vehicle. Domino effect should a deer or vehicle enters their space.