A zip archive can store its files compressed or "stored": copied in as they are. CSV compresses brilliantly, often to a fifth of its size or less. A zip that stores everything is a tarball with extra steps, and every consumer pays for the bytes.
The law
Every file in the zip is stored without compression, and together they are over 1 MB.
How to get pardoned
Use deflate, which is the default in every zip tool. In Python that is
zipfile.ZipFile(path, "w", zipfile.ZIP_DEFLATED).