While all of us know who is to blame, the idea is that an ambulance-chaser will sue the "deep pockets", the taxpayer (via the Military), as usual, and if the finding is for $10 million, and they split on 'negligence' is even 80% for the Scout Leaders' fault, the 20% remaining is still $2 Million which will get the Lawyers in the neighborhood of $1 million for themselves (50% contingency fee), or even if the contingency "fee" is 30% plus expenses, they will still get $1 million of taxpayer money as a settlement, via the Army being only a conduit to reach deep pockets.
Suing the Army in a lousy case because you think it is a "deep pocket" is not a good idea. The government has lots of lawyers on the payroll, so it doesn't cost them much to fight a lawsuit. They don't roll over quite the way private litigants do. That plaintiffs lawyer may find out he's got a tiger by the tail.