1. My understanding is that by the time Minecraft _utterly_ blew up they had a full fledged company going. Some people were probably there from the "a million or two" to "hundreds of millions" of dollars transition.
2. Notch didn't really have a lot of risk going. He wrote a game and it blew up and he hired people off the preorders.
3. Notch got lucky. It's not clear that he's an especially savvy business person, or manager, or etc. He owned most of the IP, but… he had an idea that was waiting to happen, and then it went supernova and infected the minds of most children in the western hemisphere.
If you sacrificed nights and weekends to get the thing to ship, and massaged it into production, and wrote most of the code, and strung most of the deals together, and basically made it work beyond a crashy demo… and it was all just dumb luck anyways, I think it's perfectly natural, human reaction to be resentful that your boss made an insane killing when he rage quit and didn't share much of it.
¯\_(ツ)_/¯ tricky to navigate