Actually arson would be pursued and flooding may, arson endangers the neighbors and the environment, then incurs firefighting costs which can also be pursued. Flooding ends up in stormwater and environmental violations as well as possibly damaging neigbors property (getting into that “other people’s property” area again). It’s not that it’s hard to get in trouble, it’s quite easy. It is the fact that this country was founded on individual property rights and it’s laws reflect that. Do what you like to yourself or your own stuff, stay away from others and their stuff. (actually the drug laws contradict that, but that is another argument).
The whole point is risk, those lenders gave their money away. If they stopped storing their cash in locked vaults and left piles of cash in the parking lot overnight would you feel the same pity if the homeless guys had the party of their life with the cash. That is a terrible analogy because misappropriation of found property is a crime (over $400 is a felony) but you get the point. See, pre-law wasn’t a complete waste of time after all.
