I am a hiker. While I have never lost my keys on a trail, I know people who have. I have also found other people's keys (and a wide variety of other belongings that they obviously didn't mean to drop).
It really isn't very difficult to imagine an infinite variety of objects people would like to track that might get misplaced outside of the home. If the range on AirTags are only 30 feet, then they will be useless for a lot of people who were looking forward to buying them.