[AlexITC]

The author focuses on simplicity, he tries to handle everything with a single file for the app + a single file for the database.

Unnecessary overhead gets introduced with docker, for example, now you need to depend on a container-registry + the authentication to pull those images from the server + other stuff.

[killthebuddha]

FWIW there are tons of ways to use Docker without an image (I assume you meant image) registry. If you're running Docker on the server you're deploying to then that's all you need.

[AlexITC]

I guess, still, the image needs to be built somewhere, my bet is that you will do this on the server itself, its unnecessary complexity.