Trying to find the 'real cause' is a fool's errand, because there are many places and ways to avoid the outcome.
I do take your meaning, reducing speed and following well established rules would have almost certainly have saved them.
0. PDF: http://www.leonardo-in-flight.nl/PDF/FieldGuide%20to%20Human...
In a lot of fields where the stakes are high and mistakes are costly (aviation and emergency services are the two I'm most familiar with) the analogy used is a chain. Break any link in the chain and you prevent the event.
(figuratively) The tendency to focus one's attention on one specific idea or viewpoint, to the exclusion of everything else; a one-track mind.
Road and train tunnels have many emergency exits...
"In the Swiss Cheese model, an organisation's defenses against failure are modeled as a series of barriers, represented as slices of cheese. The holes in the slices represent weaknesses in individual parts of the system and are continually varying in size and position across the slices. The system produces failures when a hole in each slice momentarily aligns, permitting (in Reason's words) "a trajectory of accident opportunity", so that a hazard passes through holes in all of the slices, leading to a failure."
A series of minor failures that combine for a serious crisis seems very relatable.
Is there a reason the throttle can't be reversed so that grabbing would reduce throttle and slow the bike?
(FWIW, I'm a fully licensed motorcyclist, don't currently ride.)