Not every company offers the same opportunities for creating value and being recognized for your contribution.
Founders and early employees have seen first-hand how enormous a single person's contribution can be. Even without being employee #1, if you've been at smaller companies, you can see both your potential value and the actual value you provided. However, employees of larger, bureaucratic companies often think their potential for recognized value to the company is stuck within a narrow, predefined range.
One reason for this difference: at smaller companies, there are more things to do than people to do them. Out of necessity, everyone wears multiple hats. This creates opportunities for efficient, self-managed, quick learners to take on new responsibilities that visibly move the company forward.