>>280509082To make it more approachable to Japanese audiences. It is an unfortunate belief in both the West and in Japan that the protagonist has to be the same nationality/ethnicity as your target audience, which then results in dumb non-sense like Tom Cruise being the main character of a movie that's about samurai in Japan.
Interestingly, China does not seem to share this belief, at least not as vehemently. They'll happily have a Hollywood star as the protag of their Chinese film if they can get one, as long as they are not from a wrong race.