“The Latte Levy” – What is the cost tipping point and why do we not always choose reusable cups?

Project title: “The Latte Levy” – What is the cost tipping point and why do we not always choose reusable cups?
Overview:

My project aims to identify the point at which cost outweighs convenience in choosing reusable vs. disposable cups. Why have we not adopted 100% reusable?