How do you explain why workers will revert back to the old way, even when the new process is more efficient for them and better for the customer?

Primarily it could be simply from habits. Habits are very powerful, and can effect new process assimilation significantly, especially if process workers had been doing the old process for a very long time. New processes and building new habits take energy and time to build.

You’ve heard the saying, “Habits are Hard to Break.” If you have any more interest in this topic, I would suggest reading the book, “The Power of Habits” by Charles Duhigg. Great book!