You'll probably find that man is not installed in a majority of the official Docker images, particularly ones that build off the official debian image. Presumably the rationale is that Docker containers are a form of app encapsulation and not something you typically log into and use interactively. It would also add a bit to the image size. The main image uses buildpack-deps which makes them kind of huge, but I don't expect adding man would add too much to the overall size.

I'm fairly neutral as to whether man should be added or not.

I did a quick comparison and adding the man-db package adds about ~10MB to the size of each image.

Seems like there isn't much appetite to add this. Should this issue be closed out?