Easy answer, spaghetti; Apple didn't build their review process for developers first, they built it for their users and Apple Inc (not necessarily in that order).

As a developer, I want free and easy access to the App store to upload my apps.

As a user, I want a selection of the safest, highest quality, predictable and elegantly design applications.

Apple Inc, as a for profitable organization, wants to ensure that they maintain control over the various revenue lines (and ensuing profit).

It's the only rational profit-maximizing-response for an organization that has their market dominance.