It just seems so backwards that making a concrete mailbox can get you sued by a jerk that intentionally drove into it. I can understand banning pitfalls and other actual traps, but why passive defensive deterrents? After all, it’s not like a bystander accidentally wandering onto your property is going to be injured by a random bolder you placed between your garden and the street.
(Edit): It seems I had a fundamental misunderstanding of US law. Thanks for indulging my curiosity!
Historically these laws exist because US law is based on English common law. I’d bet a Loonie that they exist in Canada as well for the same historical reason. If you live in a former British colony, it may be worth your time to get a basic understanding of common law.