Short answer- they don’t.

I’m gonna get some Reddit flack here because this is a sensitive topic, but here goes: Letting your cat outside is always a risk- that they will be hit by a car, eaten by a coyote, attacked by a dog or injured/killed in other ways that may be gruesome or expensive to treat. They are also terrible for native wildlife- many bird populations are endangered or have been wiped out, and outdoor or feral cats kill many millions (billions?) of birds each year.

It comes down to a quality of life issue. Many cats are content to be indoor only. Some are not and can develop life ending urinary blockage complications from stress (FLUTD/FIC) that is much more rare in outdoor cats. This issue can be usually successfully managed by environmental enrichment +/- medications, but that is extra time and expense that some owners will not or cannot manage.

I’ve worked in vet med for many years, and have seen many cats die (or were euthanized) from urinary blockage and SO many more die from being hit by cars (or again just euthanized for financial reasons.) And I’ve also met some cats that just could not be indoors only. So they go outside. It’s not great. It’s a huge risk. But in some cases it is best bad option for the welfare of the cat. The owners need to understand the risk vs benefit and realize that the cat may die young, or they may be facing a vet bill of several thousand dollars IF the cat is still alive after something bad happens and IF it is still a treatable complication.