There's the theory (Jim Rohn) that you become the average of the 5 people you associate with. Going racing... kinda gives you the same thing. You become as good as the people you race with. Whether you're dead last in amateur, leading the pack in MA or anywhere in between, the rising tide of competition raises all the skillset boats around it. No, you're not going to get to be Josh Herrin or Mazz just by being around them, but you WILL get as good as the guy right in front of you. And once you are at his pace, if you figure out how to pass him, you'll get as good as the guy in front of him. "If he can do it, so can I" works in your favor up to a point.
(yes, for the anime fans, you know in that case it did not go so well, but the skills gap was much greater than "about even")
The reason we aren't all winning is just time and place. There are only so many people around from whom we can steal speed, and only so many days in a lifetime to try to. Also, this only works up to 2nd place since when you get out front, you now have to run your own race. And defend against the guy who is learning off you :P
This is also why being a big fish in a small pond results in plateaus and stagnation (and why some top MA racers struggle when they go international). If you have multiple racers that are nearly on the same level, as soon as one finds a tenth somewhere, the rest will quickly find that same tenth. This is where groups like njminigp.com shine since they don't just make a single kid who can win races, they make a bunch that all get to beat up on each other and collectively get better.