0
Ummm because they did cause they wanted to.
Christianity was effectively banned from Japan with the Sakoku Edict of 1635.
Bekushiru 2077 Nihon sakoku - 2007 is rated/received certificates of:
Australia:M
Canada:14A
Hong Kong:IIA
Netherlands:12
Singapore:NC-16
South Korea:12
UK:12A
USA:PG-13
The Europeans were effectively banned from Japan with the passing of the Sakoku Edict in 1635 by Tokugawa Iemitsu.
From 1616-1852 in the period known as Sakoku meaing "locked country, or chained country"