You are assuming that developers have enough knowledge of Docker to deploy in production confidently. Why is it different for other ops skills? What "degree of reliability" does Docker adds over bash, for example?
It adds full environment reproducability. Essentially, "it works on my machine" -- "then we'll ship your machine". Nothing about docker in particular is meaningful, if they shipped VM images this would be identical, but docker streamlines creation and management of the entire OS image. It eliminates all differences between the developer's laptop and the production server.