cause Michael's alot like Vito. he had no aspirations to become a mobster when he was young. he's a marine & a quiet dude with morals unlike his brothers. in the flashback in part 2, Vito was the same way. just a humble family dude working at the bakery, didn't even complain or accept the gift after he got fired.
and i think it was intended to be kinda like a surprise ending, cause Michael was the furthest thing from a gangster in the beginning of the movie. Sonny was the opposite, hotheaded & got overly excited when Sollozzo introduced the drug trade. Fredo had no mobster qualities, he got embarrassed by his woman in front of his family in the beginning of pt 2
and i think it was intended to be kinda like a surprise ending, cause Michael was the furthest thing from a gangster in the beginning of the movie. Sonny was the opposite, hotheaded & got overly excited when Sollozzo introduced the drug trade. Fredo had no mobster qualities, he got embarrassed by his woman in front of his family in the beginning of pt 2