Everything is all about genetics. You don't become the best in the world if you ain't genetically more advanced than others. That applies to anything in this life, whether you're financially succesful or anything, people just have different kind of genetics to pursue for different kind of things. Some of the people tried alchohol for the first time, their brains had some sort of stimulus from it and it felt something that they can't resist meanwhile others will try them first time and never do it again, because there was something they didn't like, which again means that their brains reacted differently to it. Musicians just had the ear for the whole thing or they had the voice where people could relate to, without really having possibility to choose how their voice sounds. Even we are something like 99.9% similar to eachothers, we're still so different and as far it comes to genetics, when it comes to speed, explosiveness, strenght, stamina and so on, we're built differently. Comparing us to the animal kingdom, humans are all about endurance and being the fastest human on earth, it's a testament to humanity and it doesn't really matter whether it has been proved or not, it's still a fact until proved otherwise. If we went to that way, what you said about Bolt, we could say same about anybody or how we do know the best basketball players, tennis players or football players are the ones we're witnessing? They're just because they're geneticially more advanced than their counterparts, their mindset is different, their skill set is different, their physique is different etc, they're just special athletes and that's why they're top of the game.
On top of that, 100m dash is technical af. There's so many elements in that, that needs to be taken into the account. People often get mistaken and looking at it just being the 8 fastest guys on the final, running fast as possible without any proper knowledge about what's the best way to run from A to B. There's all the knee angles or angles in general, contact points, arm usage and so on but anyways, too tired to break it down into the pieces, you get the picture.