Without more info, it’s hard to tell.
Are there animals close by? If the way is too long (and that’s by the guests’ standars, not by ours) before they reach a habitat, they will turn around. Initially, I made my peeps walk a bit before they got to the polar bears. Just before the entrance to the cave, most of them turned around. They live for instant gratification!
Maybe there is an issue with the path? Try to delete and replace the path.