I'm curious about this as well – for the most part you usually hear about people having moved to the other way, from Chef to Ansible (personally, still using both).

Ansible also (currently) seems a bit more suited for the Docker workflow, so I'd be interested to hear about the developer's experiences with this.

I have been using Chef for a number of years.

I started this project with Ansible because I wanted to learn how to use it.

As I went along, I wanted to learn more about TDDing Chef cookbooks with Test Kitchen so I switched back to Chef.

Because Chef is awesome? (no real answer here, just a fan)