The compressed file is larger than the original because there is additional metadata or overhead added to the file during the compression process.
Files with a format like PNG are already compressed and won't benefit much from the built-in archiver. In fact, zipping PNG files may even increase the file size because every compression method, including zipping, introduces some overhead for tracking file information, structure, and other properties and overhead takes up space.
I suggest you try iBoysoft MagicMenu. It allows you to right-click the PNG files on Mac and zip them with a selected compression level. You can choose the high level to make the size smaller.