LogFAQs > #979863766

Most of the samurai rituals and Bushido stuff is post Sengoku. Basically once samurai were bureaucrats they had to start coming up with stuff to help justify their existence as a higher class in a peaceful country.

Shogun though is fiction loosely based on real history, so this sort of thing is pretty whatever. Ghosts of Tsushima also inserted a lot of Bushido and other ahistorical stuff even farther into the past and people still largely liked it.