The goal of an ecosystem's leader is not to take the biggest possible cut, but rather to grow the ecosystem as much as possible, knowing that this is the best long term option both for them and for everyone else who participates.
For example, Google benefits more from growing the web and thus inventory than from taking more of a cut from existing advertisers. A city benefits more from growing the incomes of its residents than from taxing them at a higher rate. And while some sellers will disagree, Amazon really is trying to take as small as a cut as possible if that's what grows the business.
An interesting question. Does a small player in a larger ecosystem also benefit from growing the ecosystem rather than maximizing their short term cut?