Like many parts of life, bushwalkers can be group by ability - total bumbly to the heavy end of the spectrum, very fit, good gear, good judgement and a lot of experience. On balance of probability, the first classification is likely to need help for a very simple blunder, and the latter will only need help in dire and exceptional circumstances.
It used to be that road prangs were called accidents. No more. An accident is avoidable, so being drunk, having an unroadworthy vehicle, failing to indicate, exceeding the posted speed limit or a speed suitable for the conditions, and diverging laterally when unsafe are avoidable. Any prang so caused is not an accident - it's a collision.
Alternatively, a flat tyre, a heathy driver having a heart attack or a seizure, or an otherwise sound vehicle having a mechanical failure leading to a prang would probably be classified as accidents.
The bumbly walker is an accident waiting to happen. The heavy end walker is most probably at risk from unavoidable circumstances. In both cases the only way to minimise risk is to stay home.
If the bumbly walker is invoiced, how does the one know where to stop on the bumbly-heavy spectrum? I do not have an answer for that.
Police Rescue are on standby at all times. It could be a prang on the M1, an industrial incident, or a boat that is sinking. While there are certainly costs for the rescues, I'm advised that the extra costs for each rescue are small compared to the standing costs.
Better education and better signs at parks would go a long way to assist. And at times, better management by other agencies.