I don't think that handy bit of knowledge has made it into the 'how to make a tree swing' manual yet but it really ought to. Also should be in 'proper care of your tree swing' over the years and the periodic inspection.
If you as an individual want to own trees, and especially if you want to let others use your property, I don't see any reason why you should be held to a lesser standard of care than any municipality across the country. If you can't afford to keep your trees safe then you can't afford the trees and/or the property.
But yeah, this definitely isn't anything beyond what you'd learn in a plant pathology 101 class in college or a basic arborist certification.
1. Handling it like that might mean more cut down trees, which is probably not something the town/city has an interest in. (Maybe they should send professionals to check out all the trees?)
2. Properties can change hands much quicker than cut down trees can be regrown.
I am not sure what the point of point 2 is, when you have point 1. You don't really have to cut down all the untested trees on your property, but if you're not doing testing/maintenance on the trees for ANY reason(ignorance, cost), don't be surprised when one kills someone and you're held liable for it. You should consider this before buying a property with trees. It's similar to owning a dog. If you own a dog, and it runs out and bites someone, you will likely be held liable, and the dog will likely be put down. If the dog tests positive for rabies before even biting anyone, it will be put down, similar to a dead tree being cut down.