If I’m updating the source code already I might as well build my service from it, I really don’t see how building a docker container afterward makes it easier considering the update can also break compatibility with the docker environment.
Also adapting can be a pita when the package is built around a really specific environment. Like if I see that the dockerfile installs a MySQL database can I instead connect it to my PostgreSQL database or is it completely not compatible? That’s not really something the dockerfile would tell me.