There are some places in musicbrainz-docker/musicbrainz-dockerfile/Dockerfile where the setup process doesn't clean up after itself well, causing the image to be larger than expected:
https://github.com/metabrainz/musicbrainz-docker/blob/21c9b4f6f307c0152572142960454d1f5245f9f2/musicbrainz-dockerfile/Dockerfile

Line 10, apt-get install doesn't rm -rf /var/lib/apt/lists/* afterwards
Line 34 Yarn installation, the same
Line 79 apt-get clean and rm will remove the content from the final image, but it will still be there in intermediate images, contributing to the final image size. These commands should be run after the relevant RUN command that adds each file
Line 26 installs postgres - I think this is the server? In the case of the musicbrainz image this probably only needs the client.