There is already a book that details the origin story, but like most things, happenstance and early opportunities play a big role.
Carmack would have never met Romero or the others, who first worked for SoftDisk, and were later allowed to cherry pick “cool” kids willing to work crazy overtime and spin out their own business unit called Gamers Edge, much to the dismay of the senior developers. That’s where they made Keen originally. According to the story, the rest of the developers actually did “organize” and threatened to quit en masse because they were jealous of the special treatment that Carmack and Romero were getting. The owner had to tell them, like it or not, Gamers Edge was what was paying their salaries and he had no choice.
iD would not have existed without Gamers Edge, and Gamers Edge would not have existed without SoftDisk.
Wolf3d and Doom would not have existed without both of them. And the world would be very different without those.
Carmack is smart and might have done something else cool, perhaps in a different industry with a different group, but it wouldn’t have been Wolfenstein or Doom. He would have been unemployable because he could not stand college, and he would likely not have started his own company, because business and management was what he detested and relied on his partners for.
https://en.m.wikipedia.org/wiki/Softdisk