Insurance needs to be blanket coverage as there are just too many unforseens to be able to list each and all variations. Much like 3rd Party cover for your car.
But this isn’t compulsory third-party car insurance. I realise insurance (or lack thereof) is used as a dubious excuse to restrict people from eveything from overcrowded bars to bouncy castles. In this case, I guess you’d have to look at the policy and see what it says. But, yes, I have heard of intruders into private property suing for damages when they injured themselves on something that was unsafe. Or maybe that’s an urban myth.