A bit odd that they didn't include Japan in their set of countries. My expectation is that it would have probably topped the list.
replies(4):
https://onlinelibrary.wiley.com/doi/abs/10.1111/1540-5893.37...
Abstract
This article examines the lost property regime of Japan, which has one of the most impressive reputations in the world for returning lost property to its rightful owner, and compares it with that of the United States. Folk legend attributes Japanese lost‐and‐found success to honesty and other‐regarding preferences. In this article, I focus on another possible explanation: legal institutions that efficiently and predictably allocate and enforce possessory rights. These recognized, centuries‐old rules mesh with norms, institutional structures, and economic incentives to reinforce mutually the message that each sends and yields more lost‐property recovery than altruism alone.