I agree that being a leader in the field does offer flexibility and choice. But I don't think that's always (or even mostly) why people work to that position. They do it because they LIKE writing and speaking, or because networking is a key part of their responsibilities.

I'm a nuts and bolts, head and shoulders deep in code kind of guy. The stuff that gets my crank going never requires an audience. TOP-of-field is my career ambition. Being so good at what I want to do that people will pay me to do it.