I dunno man, that looks like just about nothing would have covered it. Comprehensive would have covered the straps unexpectedly failing, or the hitch failing, or the moon falling on your bike but because you were in control of the vehicle at the time and there's a big questionmark on whether you strapped it down perfectly, I'm not sure even comprehensive would cover this. Liability insurance is carried by automotive transportation companies for this reason, but that's different too.
Insurance is a messed up business. Like if I avoid hitting a lamborghini who merged in front of me but in the process destroy my $50 jacket, that's not covered, but if I instead hit the lamborghini, destroy my motorcycle in the process and also my jacket, then I get money for both the jacket and the motorcycle. I swear they're literally in the business of being evil.
Back in Australia, when you took your bike to the AHG track for rider training days, you were not insured on the track. It was generally one of those unspoken things that no one ever crashed on the track, but we all witnessed them crashing on the first roundabout outside of the track.