Rather than learn a few styles of jujitsu and safe guard the authenticity of the techniques, he melded them, modified a few and applied a new concept to it. The techniques were now for exercise, recreation or even self defence but now, the latter was not the overriding objective. Nor was learning it for the reason of maiming and killing, although they still could do those, with a modicum of modification
But that wasn't enough. Unlike a lot of the people of his day, he saw a world outside Japan that..and this is the important bit...could benefit from the practice of Judo. Not defeated in competition to prove the superiority of the Japanese race (although I have no doubt there were a few who though that as there are those who still think that these days whether in regard to Judo or other arts), but because it could enhance the quality of their lives, irregardless of whether they were Japanese were not.
The codified techniques meant that there were no 'secret' techniques held back to ensure dominance by one group over another. Randori practice meant that even if this occured, it would be for a short while until the counterweight would shift in the opposite direction. And because there were no real secrets save for hard, regular dedicated practice - everyone could do it. Thus, it spread to the world
Being made an Olympic sport did not hurt it's chances either. But one great thing about Judo, is that in not overly pushing the cultural element, it ironically enabled it to be embraced in far greater numbers and I am sure, has done a lot more to carry a slice of Japanese culture to the world that many would not have been exposed to.