I also don’t see a water skier under a sling load 100% of the time. Also last time I looked a sling endorsement doesn’t authorise a pilot to tow a water skier. There is a reason for this. Because it’s reckless.
Obviously it's not seen 100% of the time. It does seem to have crossed the mind (and video cameras) of those with both water skiing and helicopter experience, though. The sling endorsement doesn't authorise a pilot to tow a skier - but the point is:
is there any legislation forbidding it?.
After all, live loads on slings are not forbidden (otherwise helicopter rescue wouldn't be possible). Dragging things is not forbidden... Is it "reckless"? - I am not aware of any heli-water skiing injuries, so it can't be that much of a problem.
I think that it is one of those things which LOOK "exciting", but are pretty mundane when performed by knowledgeable people.
Now having said that, it doesn't exclude the allegations of leaving a helicopter running with passengers on board but no pilot etc etc.