Seems there’s a problem in the way Japan legislates workplace insurance:

Under Japanese corporate law, companies are required to insure their employees against workplace accidents and this insurance extends to cover commuting to and from work, despite this few employee insurance policies include cycling insurance. As a result employers in Japan implement company policies which prevent their employees from cycling to work to protect themselves from financial liability should an accident occur.

For a more fullsome explanation go to tokyobybike blog.

Japan’s National Bike to Work Ban ~ Tokyo By Bike