Investment... It's a bit too simple to just say money, but investment wraps it up better. Chips may not be open source, but they are physically there to be taken apart and reproduced. That's what a lot of those Chinese knockoff chips are (baring the ones where the designs are outright stolen). The only thing that stops you from doing the same thing as those bootleg fabs is being willing to soak time and resources into the project. It's just a big project. Like a Bloomfield i7 (which is old and fairly large) has 731 million transistors in it...