Business outside of IT works and innovates slowly.
Try to explain your average 50-year-old middle manager in ManufacturingCorp why Docker (or anything conceived in the last, say, 5 years) is a good idea even when implementation costs money instead of staying with what is known and appears risk-free at no extra cost.
This is a huge factor. Newer companies/startups are starting to use Docker, but it will be very difficult to come into a company that is already running and convince them to change their entire workflow/infrastructure over to something different.
I think over the next few years you will see a lot more docker infrastructures in production as these newer applications begin to mature.
Try to explain your average 50-year-old middle manager in ManufacturingCorp why Docker (or anything conceived in the last, say, 5 years) is a good idea even when implementation costs money instead of staying with what is known and appears risk-free at no extra cost.