When you learned about that, you did not read the entire paragraph: being captured was traditionally considered a dishonor (for the past 500 years, at least), i

When you learned about that, you did not read the entire paragraph: being captured was traditionally considered a dishonor (for the past 500 years, at least), it is a huge failure for a soldier (or samurai). Ritual suicide is the solution to that dishonor. There are degrees of failure, some is considered to be beyond fixing.