A limited lifespan. Sometimes I think Bill Gates might be twice as smart as I am. That means he's worth two Dave Winers, not ten billion. There's only so much growing a single human being can do. Why one entrepreneur hits a home run and another languishes has more to do with the times, and how the team of people behind the front-person executes.
All companies are dysfunctional.
Part of the dysfunction is the idea that the company is realized in a single brain. I still believe some brains resonate with the world more effectively than others, and some brains can teach other brains how to resonate. Yes it matters, very much, who is leading a company. Luck plays a big role too. Most of the heroes we look up to were good at picking up other people's ideas, not synthesizing their own.