For the second year in a row, Japan is ranked on top of the Henley & Partners Passport Index. The nation’s passport-bearing citizens can travel to 190 of the 199 countries and regions in the world without having to obtain a visa in advance. This privilege is shared by Singaporeans, who share first place with Japan in the passport ranking, published by the British citizenship consultancy firm.

But having the freedom to jet anywhere in the world with such ease appears to be lost on the Japanese. As Nikkei Asian Review points out, only 23% of Japanese citizens actually have a passport—the lowest among G7 states. This mirrors the modest growth in overseas travel for Japanese tourists since 2015. And when they do travel, the Japanese tend to stay close to home, preferring to visit places like South Korea, Taiwan, Hong Kong, and Macau.

Why are so many Japanese disinterested in going beyond their borders? One big reason analysts cite is the challenge of international travel for the country’s large aging population. As for why Japanese youth are less likely to go abroad, immigration expert Xiaochen Su has a curious theory. Writing for the Japan Times in March, Su explained:

Chikyu no arukikata (“How to Walk the Earth”) has been the best-selling Japanese travel guide for the past 35 years, with 8 million copies published…The greater lengths that [the book] devotes to potential crimes in travel destinations serve as a psychological deterrent for potential Japanese travelers and entrench an already present belief among Japanese youths about foreign countries being significantly more dangerous than Japan, with Japanese travelers targeted by criminals.

Japan is a remarkably safe country, with cities like Tokyo and Osaka often ranked among the world’s safest cities.

Meanwhile, more foreigners are trooping to Japan. A recent UN World Tourism Organization report shows that international tourism to the country increased by 250% between 2012 and 2017. The trend will likely continue with the 2020 Tokyo Olympic Games, expected to attract a million visitors a day to the capital. Masses of tourists are coming despite the burden of obtaining a travel visa—Japan has a waiver program with only 68 countries.